Recombinant Mouse Serine/threonine-protein phosphatase 2A 55 kDa regulatory subunit B gamma isoform (Ppp2r2c)

What is PPP2R2C and what is its role in the PP2A complex?

PPP2R2C (also known as PR55/Bγ) is a substrate-binding regulatory subunit of the protein phosphatase 2A (PP2A) holoenzyme complex. It functions within the PP2A heterotrimer to provide substrate specificity and subcellular localization. The PP2A holoenzyme typically consists of a structural A subunit, a catalytic C subunit, and a regulatory B subunit (such as PPP2R2C) .

The regulatory B subunits are particularly important as they determine which substrates will be dephosphorylated by the PP2A complex. PPP2R2C belongs to the B55/PR55/B family of regulatory subunits and appears to have tissue-specific functions, with particularly important roles in the brain and prostate tissue .

How does PPP2R2C contribute to cellular phosphorylation balance?

PPP2R2C regulates the dephosphorylation of specific substrates by directing the PP2A catalytic subunit to these targets. In neuronal tissues, PPP2R2C has been shown to regulate tau dephosphorylation, with decreased PPP2R2C expression leading to increased tau phosphorylation, a hallmark of Alzheimer's disease and other tauopathies .

In experimental cell models, modulation of PPP2R2C expression directly affects PP2A activity, confirming its regulatory role in phosphorylation balance. Studies in cultured cells demonstrate that PPP2R2C expression regulates PP2A activity and tau dephosphorylation, with knockdown of PPP2R2C resulting in altered phosphorylation patterns of downstream targets .

What distinguishes PPP2R2C from other PP2A regulatory subunits?

While several regulatory subunits direct PP2A activity, PPP2R2C has distinct tissue expression patterns and substrate preferences. Unlike PPP2R2A (PR55/Bα), which is more broadly expressed and considered the major tau phosphatase, PPP2R2C shows enriched expression in brain tissue and appears later in development .

PPP2R2C also has unique roles in cancer biology that differ from other regulatory subunits. For example, while both PPP2R1A and PPP2R2C are downregulated in prostate cancer, PPP2R2C specifically promotes androgen-independent growth when suppressed, indicating distinct regulatory functions in cancer progression pathways .

What is the tissue distribution pattern of PPP2R2C expression?

PPP2R2C exhibits a predominant expression in brain tissue, making it a brain-enriched isoform of the PP2A regulatory subunit. Research in wild-type mice has shown that PPP2R2C is primarily expressed in neural tissues, with particularly high expression in the brain .

How does PPP2R2C expression change during development and aging?

PPP2R2C expression shows distinct temporal patterns during development and aging. In mouse models, PPP2R2C expression increases during brain development and exhibits differential patterns between wild-type and Alzheimer's disease (AD) transgenic mice .

The differential expression of PPP2R2C between wild-type and AD mice becomes apparent during adulthood, coinciding with the onset of AD symptoms. This suggests that PPP2R2C dysregulation may be involved in age-related neurodegeneration. Additionally, even in non-neural tissues where PPP2R2C is expressed at low levels, its expression tends to increase with age, pointing to potential roles in the aging process .

What factors regulate PPP2R2C expression?

Research has identified several regulators of PPP2R2C expression. One notable regulator is the telomeric protein TRF2, which positively regulates PPP2R2C expression. Importantly, TRF2 expression decreases in Alzheimer's disease patients, which may contribute to the reduced PPP2R2C levels observed in AD .

The regulation of PPP2R2C involves complex genetic and epigenetic mechanisms. Single-nucleotide polymorphisms (SNPs) in the PPP2R2C gene have been associated with several mental disorders, suggesting genetic variation influences its expression and function. Additional regulatory mechanisms may include transcription factors, microRNAs, and post-translational modifications, though these require further investigation .

How does PPP2R2C function as a tumor suppressor in prostate cancer?

PPP2R2C functions as a tumor suppressor in prostate cancer through multiple mechanisms. High-throughput RNA interference (RNAi) screening identified PPP2R2C as one of 40 genes whose knockdown promoted proliferation of prostate cancer cell lines (LNCaP and VCaP) in the absence of androgen. This indicates that normal PPP2R2C expression suppresses androgen-independent growth, a hallmark of aggressive prostate cancer .

Importantly, PPP2R2C appears to be downregulated in both primary and metastatic prostate cancers compared to benign prostatic tissue. Immunohistochemical analysis of PPP2R2C protein levels in primary prostate tumors demonstrated that low PPP2R2C expression significantly associated with an increased likelihood of cancer recurrence and cancer-specific mortality, further supporting its tumor-suppressive role .

What mechanisms enable castration-resistant growth following PPP2R2C loss?

The mechanisms by which PPP2R2C loss promotes castration-resistant prostate cancer growth appear to be independent of canonical androgen receptor (AR) signaling. Experimental evidence shows that loss of PPP2R2C promotes androgen ligand depletion-resistant prostate cancer growth without altering AR expression or canonical AR-regulated gene expression .

Furthermore, cell proliferation induced by PPP2R2C loss was not inhibited by the AR antagonist MDV3100, indicating that PPP2R2C loss promotes growth through pathways independent of AR-mediated transcriptional programs. This suggests PPP2R2C regulates alternative growth pathways that can bypass the need for AR signaling, allowing cancer cells to proliferate even during androgen deprivation therapy (ADT) .

What signaling pathways are affected by PPP2R2C suppression in cancer cells?

Researchers have investigated several candidate pathways that might be regulated by PPP2R2C in cancer. Interestingly, knockdown of PPP2R2C did not result in SRC phosphorylation in prostate cancer cell lines, and treatment with the SRC inhibitor Dasatinib failed to inhibit castration-resistant growth induced by PPP2R2C knockdown. This indicates that SRC activation is not the mechanism by which PPP2R2C loss promotes androgen-independent growth .

Additionally, studies evaluated the influence of PPP2R2C in other signal transduction pathways postulated to influence castration-resistant prostate cancer growth, including extracellular signal-regulated kinase 1/2 (ERK1/2) and Protein Kinase B/AKT (AKT) pathways. The data suggests that PPP2R2C regulates alternative, potentially novel signaling pathways that deserve further investigation .

The following table summarizes the effects of PPP2R2C knockdown on various cancer-related pathways:

How does PPP2R2C contribute to tau phosphorylation regulation in Alzheimer's disease?

PPP2R2C plays a critical role in regulating tau phosphorylation in the brain. Tau hyperphosphorylation is a key pathological feature of Alzheimer's disease (AD) and other tauopathies. While PP2A is known to be the main phosphatase involved in dephosphorylating tau, the specific regulatory subunits involved in this process are still being elucidated .

Research has demonstrated that PPP2R2C expression is downregulated in the aged AD mouse brain compared to wild-type mouse brain. In cultured cells, experimental modulation of PPP2R2C expression directly affects PP2A activity and tau dephosphorylation. When PPP2R2C expression is reduced, tau phosphorylation increases due to decreased PP2A-mediated dephosphorylation activity. These results suggest that dysregulation of PPP2R2C expression may be involved in the onset of AD by contributing to the hyperphosphorylation of tau protein .

What is the spatiotemporal expression pattern of PPP2R2C in normal versus AD brain?

Studies measuring the differential spatiotemporal expression patterns of PPP2R2C in wild-type and transgenic AD mice have revealed important differences. While PPP2R2C is expressed in the brain of both wild-type and AD model mice, its expression is downregulated in the aged AD mouse brain compared to the wild-type mouse brain .

The differential expression of PPP2R2C between wild-type and AD mice becomes apparent during adulthood, coinciding with the onset of the first AD symptoms in these mice. This temporal correlation suggests that decreased PPP2R2C expression may contribute to AD pathogenesis rather than merely being a consequence of the disease. Future studies examining PPP2R2C expression in different brain regions and at various disease stages would provide more detailed information about its spatiotemporal regulation in AD .

How do PPP2R2C polymorphisms influence neurological function?

Single-nucleotide polymorphisms (SNPs) in the PPP2R2C gene have been associated with several mental disorders, suggesting that genetic variation in this gene may influence neurological function. While the specific mechanisms by which these polymorphisms affect PPP2R2C function are not fully understood, they likely alter PPP2R2C expression levels or the protein's ability to interact with its substrates .

Given that PPP2R2C is involved in tau dephosphorylation, polymorphisms that reduce its expression or function could potentially increase susceptibility to tauopathies like Alzheimer's disease. Further research is needed to characterize the specific effects of different PPP2R2C polymorphisms on PP2A activity, tau phosphorylation, and neurological function .

What are effective techniques for measuring PPP2R2C expression and activity?

Several complementary techniques can be used to effectively measure PPP2R2C expression and activity:

What experimental models are most suitable for studying PPP2R2C function?

Various experimental models have proven valuable for studying different aspects of PPP2R2C function:

• Cell Line Models: Prostate cancer cell lines such as LNCaP and VCaP have been used to study PPP2R2C's role in androgen-independent growth. Neuronal cell lines are useful for studying its role in tau dephosphorylation .

• siRNA Knockdown: RNA interference using siRNAs targeting PPP2R2C has been effective for studying loss-of-function phenotypes. This approach revealed that PPP2R2C knockdown promotes androgen-independent growth in prostate cancer cells and affects tau phosphorylation in neuronal models .

• Transgenic Mouse Models: Alzheimer's disease transgenic mice have been used to study PPP2R2C expression patterns in normal versus disease states. These models show downregulation of PPP2R2C in aged AD mouse brain compared to wild-type .

• Human Tissue Samples: Analysis of PPP2R2C expression in patient-derived tissues, including prostate cancer samples and potentially post-mortem brain tissues from AD patients, provides clinically relevant insights into PPP2R2C's role in disease .

How can RNA interference be optimized to study PPP2R2C function?

Optimizing RNA interference for studying PPP2R2C function involves several considerations:

• siRNA Design: Multiple siRNAs targeting different regions of the PPP2R2C transcript should be used to confirm specificity. In published studies, researchers validated results using at least two different siRNAs (e.g., siRNA #2 and siRNA #3) that achieved 84-96% knockdown efficiency .

• Transfection Optimization: Cell type-specific transfection conditions should be established to maximize knockdown efficiency while minimizing toxicity. Parameters to optimize include transfection reagent type, reagent concentration, cell density, and incubation time.

• Knockdown Validation: Both mRNA (qRT-PCR) and protein (Western blot) levels should be assessed to confirm PPP2R2C knockdown. In published studies, PPP2R2C transcripts were reduced 6.7-fold by siRNA #2 and 4.2-fold by siRNA #3 in VCaP cells .

• Functional Readouts: Appropriate phenotypic assays should be selected based on the cellular context. For prostate cancer cells, proliferation assays in androgen-depleted medium are effective (showing 33-72% increased growth following PPP2R2C knockdown). For neuronal cells, measurements of tau phosphorylation would be appropriate .

• Controls: Include both negative controls (non-targeting siRNA) and positive controls (siRNA targeting a gene with known phenotype) to validate experimental setup.

What strategies could restore PPP2R2C function in cancer or neurological disorders?

Several potential strategies could restore PPP2R2C function or compensate for its loss:

• Gene Therapy Approaches: Direct restoration of PPP2R2C expression through gene therapy could potentially reverse the effects of PPP2R2C loss in both cancer and neurological disorders. This would involve delivering functional PPP2R2C genes to affected tissues.

• Targeting Upstream Regulators: Enhancing the expression or activity of positive regulators of PPP2R2C, such as the telomeric protein TRF2, could indirectly increase PPP2R2C levels. This approach has been suggested for Alzheimer's disease, where TRF2 expression is decreased in patients .

• Small Molecule Activators: Developing small molecules that can enhance the activity of remaining PPP2R2C-containing PP2A complexes might compensate for reduced PPP2R2C expression. This approach would require detailed understanding of PPP2R2C structure and function.

• Targeting Downstream Pathways: Identifying and inhibiting the growth pathways activated by PPP2R2C loss represents another therapeutic strategy. While SRC, PI3K, and ERK1/2 pathways do not appear to be the primary mechanisms in prostate cancer, other downstream effectors remain to be discovered .

What are the challenges in developing PPP2R2C-targeted therapeutics?

Developing therapeutics targeting PPP2R2C faces several significant challenges:

• Lack of Enzymatic Activity: As noted in the research, "PPP2R2C does not carry an intrinsic enzymatic activity, [so] its pharmacological targeting might be difficult" . Most small molecule drugs target enzymes or receptors with active sites, making direct PPP2R2C targeting challenging.

• Tissue Specificity: PPP2R2C has important functions in multiple tissues, particularly the brain. Therapeutic approaches must achieve tissue-specific effects to avoid unintended consequences in non-target tissues.

• Pleiotropic Effects of PP2A: PP2A plays diverse roles throughout the body, as researchers note: "PP2A plays pleiotropic roles in various organs, indicating the need for therapeutic strategies specific to PP2A enzyme in the brain, to avoid severe secondary effects" . This complexity increases the risk of off-target effects.

• Understanding Downstream Mechanisms: The precise mechanisms by which PPP2R2C loss promotes disease progression are not fully understood. As noted in prostate cancer research, PPP2R2C loss promotes growth independently of several well-characterized pathways (AR, SRC, PI3K, ERK1/2) . Better characterization of these mechanisms is needed.

How might PPP2R2C biomarkers be used in personalized medicine approaches?

PPP2R2C holds potential as a biomarker for personalized medicine approaches in several ways:

• Prognostic Biomarker in Prostate Cancer: Immunohistochemical analysis has shown that low PPP2R2C expression in primary prostate tumors significantly associates with increased likelihood of cancer recurrence and cancer-specific mortality. This suggests PPP2R2C could serve as a prognostic biomarker to identify patients at higher risk of aggressive disease who might benefit from more intensive monitoring or treatment .

• Predictive Biomarker for Treatment Response: PPP2R2C status might predict response to androgen deprivation therapy (ADT) in prostate cancer. Tumors with low PPP2R2C expression may be more likely to develop castration resistance through AR-independent mechanisms, suggesting these patients might benefit from additional therapies beyond ADT .

• Risk Assessment in Neurological Disorders: Given the association between PPP2R2C polymorphisms and mental disorders, genetic screening could potentially identify individuals at higher risk for certain neurological conditions. This could facilitate earlier intervention or preventive measures .

• Treatment Selection: If therapies targeting PPP2R2C or its regulated pathways are developed, measuring PPP2R2C expression levels could help select patients most likely to benefit from these approaches. Additionally, monitoring PPP2R2C levels during treatment could potentially serve as a marker of treatment efficacy.