KLHDC8B Human

What is the molecular structure of KLHDC8B?

KLHDC8B (Kelch Domain-Containing 8B) is a gene encoding a protein predicted to contain seven kelch repeat domains. These kelch domains fold into β-propeller structures capable of participating in protein-protein interactions. The protein consists almost entirely of these seven kelch repeats, making it a specialized member of the larger family of kelch repeat-containing proteins that have diverse cellular functions .

Where is KLHDC8B expressed in human cells?

KLHDC8B is widely expressed across tissues but demonstrates specific temporal expression patterns during the cell cycle. Among lymphocytes, KLHDC8B is expressed most strongly in germinal center B cells, which are the cells of origin for classical Hodgkin lymphoma. At the subcellular level, KLHDC8B accumulates most strongly in mitotic cells and concentrates in the midbody of the cytoplasmic bridge linking daughter cells as they are about to separate during cytokinesis .

How is KLHDC8B expression regulated during the cell cycle?

KLHDC8B exhibits tightly controlled cell cycle-dependent expression. Studies using synchronized HeLa cells have demonstrated that KLHDC8B is transcribed predominantly during S phase, translated exclusively during mitosis and cytokinesis (when the 4N population is transitioning to 2N), and is rapidly degraded after cell division. This precise temporal regulation suggests a specific function related to cell division completion .

What genomic alterations of KLHDC8B have been associated with human diseases?

Several genomic alterations of KLHDC8B have been identified in association with classical Hodgkin lymphoma:

These alterations collectively suggest that reduced KLHDC8B expression contributes to cHL development .

How does reduced KLHDC8B expression contribute to lymphomagenesis?

Reduced KLHDC8B expression appears to disrupt normal cytokinesis, leading to the formation of binucleated cells. This directly recapitulates a hallmark of classical Hodgkin lymphoma—the binucleated Reed-Sternberg cells. These cells form as a consequence of defective cytokinesis rather than through cell fusion. This aligns with Boveri's hypothesis that defective cytokinesis promotes tumorigenesis through the formation of genetically unstable tetraploid cells. The resulting genomic instability may drive oncogenic transformation in B cells, contributing to lymphoma development .

Does the 5′-UTR variant affect KLHDC8B function independently of protein levels?

The 5′-UTR variant at position +28 (C→T) is located within a poly(C) repeat cluster. RNA-binding, KH domain-containing proteins recognize poly(C) repeats and participate in cap-independent translation. Significantly, KLHDC8B is translated only during mitosis and cytokinesis, when cap-dependent translation is extinguished and only cap-independent translation is available. The 5′-UTR variant likely disrupts KLHDC8B's mitotic expression. Complementation studies support this hypothesis, as cDNA lacking the 5′-UTR cannot fully rescue the binucleation defect, suggesting the 5′-UTR plays a functional role beyond simply affecting protein levels .

What experimental methods have been used to characterize KLHDC8B's role in cytokinesis?

Researchers have employed multiple complementary approaches to elucidate KLHDC8B's function:

These methodologies collectively provide strong evidence for KLHDC8B's essential role in cytokinesis completion .

How can researchers identify KLHDC8B mutations in patient samples?

Several complementary molecular approaches are used to detect KLHDC8B alterations:

• FISH to map bacterial artificial chromosomes spanning chromosomal breakpoints

• Southern blot hybridization with probes from candidate genes to narrow intervals containing breakpoints

• Long-range PCR and progressively refined PCR to further narrow intervals

• DNA sequencing to define precise breakpoints

• Array-based comparative genomic hybridization to exclude possible cryptic rearrangements

• Quantitative real-time RT-PCR to measure gene expression levels

• Western blot to confirm corresponding protein expression levels

• Loss of heterozygosity (LOH) analysis using SNPs from within and flanking the gene

These techniques must be applied carefully, as Reed-Sternberg cells comprise only a minute fraction of Hodgkin lymphoma tumors .

What RNA interference approaches have proven most effective for studying KLHDC8B function?

The most effective RNA interference approaches for KLHDC8B include:

• Short hairpin RNAs (shRNAs) targeting different regions of KLHDC8B mRNA, with efficacy correlating with the degree of binucleated cell production

• siRNAs targeting either the 5′- or 3′-UTR of the endogenous gene

• Complementation with RNAi-resistant forms of KLHDC8B cDNA lacking the targeted regions

Importantly, researchers must confirm specificity by testing multiple shRNAs and demonstrating that the degree of binucleation correlates with silencing efficiency. Complementation experiments are critical to rule out off-target effects .

How does KLHDC8B relate to other kelch domain-containing proteins involved in cytokinesis?

KLHDC8B belongs to a broader family of kelch domain-containing proteins with roles in cytokinesis:

• The kelch domain was initially discovered in Drosophila as a repeated element in actin-organizing proteins forming "ring canals" that interconnect germ cells after incomplete cytokinesis

• Coiled-coil kelch proteins Kel1p and Kel2p and Tea1p function in positioning the cell division plane in yeast

• The mammalian BTB/POZ-kelch protein Keap1 localizes to the midbody's central matrix

• BTB/POZ-kelch proteins KLHL9 and KLHL13 associate with the Aurora kinase spindle checkpoint regulator at the midbody

• Silencing of Keap1, KLHL9, and KLHL13 similarly increases binucleated cell formation

This evolutionary conservation suggests a fundamental role for kelch domain proteins in cytokinesis across species .

What is the evidence supporting KLHDC8B as a potential tumor suppressor gene?

Multiple lines of evidence support KLHDC8B's potential role as a tumor suppressor:

• Constitutional translocation disrupting KLHDC8B segregates with classical Hodgkin lymphoma in a family

• A 5′-UTR variant reducing KLHDC8B expression is associated with familial cHL (OR 4.64)

• LOH for KLHDC8B has been detected in Reed-Sternberg cells from sporadic cHL cases

• Reduced expression leads to binucleated cell formation, consistent with Boveri's hypothesis on defective cytokinesis promoting tumorigenesis

• The 3p21.31 region where KLHDC8B resides is frequently deleted or rearranged in B-cell lymphomas and other malignancies

• Genetic linkage analysis had previously mapped a predisposition locus for nasopharyngeal carcinoma (another EBV-associated malignancy) to the vicinity of 3p21.31

These findings suggest KLHDC8B may have broad relevance in cancer development .

What is the relationship between KLHDC8B and other midbody proteins implicated in cancer?

KLHDC8B's role in cancer suggests midbody proteins may represent a general class of tumor suppressors. This hypothesis is supported by observations that other crucial proteins involved in cytokinesis are also implicated in cancer development:

• BRCA1 and BRCA2, in addition to their well-established roles in DNA repair, also localize to the midbody during cytokinesis

• BRCA1-associated protein BARD1 is likewise found at the midbody

• Somatic mutations of KEAP1 (another midbody protein) are frequent in lung cancer

• The 3p21.31 region shows frequent deletions in lung cancer and other malignancies

These associations suggest a mechanistic link between cytokinesis defects and cancer development that extends beyond KLHDC8B alone .

What are the key technical challenges in studying KLHDC8B in Hodgkin lymphoma?

Several technical challenges complicate the study of KLHDC8B in Hodgkin lymphoma:

• Reed-Sternberg cells comprise only a minute fraction of the tumor in classical Hodgkin lymphoma

• KLHDC8B is only expressed during specific phases of the cell cycle, making timing crucial for detection

• The protein is rapidly degraded after cell division, necessitating precise experimental timing

• Cap-independent translation during mitosis complicates the study of translational regulation

• Multiple mechanisms may affect KLHDC8B function, requiring diverse experimental approaches

• Distinguishing KLHDC8B-specific effects from general cytokinesis defects requires carefully controlled experiments

These challenges necessitate specialized techniques such as fluorescence-activated cell sorting to isolate rare Reed-Sternberg cells and sophisticated cell synchronization protocols .

How might KLHDC8B research influence cancer therapeutic development?

Understanding KLHDC8B's role in cytokinesis and cancer development opens several potential therapeutic avenues:

• Targeted therapies aimed at restoring normal KLHDC8B function or expression levels in tumors with reduced expression

• Exploiting synthetic lethality approaches in cells with KLHDC8B deficiency

• Developing biomarkers based on KLHDC8B status to identify patients at risk for developing Hodgkin lymphoma

• Screening family members of cHL patients for KLHDC8B alterations as part of genetic counseling

• Exploring the broader class of midbody proteins as potential cancer therapeutic targets

While these approaches remain theoretical, the clear link between KLHDC8B dysfunction and binucleated Reed-Sternberg cell formation provides a compelling biological rationale for further investigation .

What directions should future KLHDC8B research pursue?

Future research on KLHDC8B should focus on:

• Determining the protein interaction partners of KLHDC8B at the midbody during cytokinesis

• Identifying the specific molecular mechanisms by which KLHDC8B participates in cytokinesis completion

• Investigating somatic KLHDC8B alterations in a larger cohort of sporadic cHL cases

• Exploring KLHDC8B status in other cancer types with frequent 3p21.31 alterations

• Developing mouse models with KLHDC8B disruption to study its role in lymphomagenesis in vivo

• Investigating potential connections between EBV infection and KLHDC8B function, given the association with EBV-related malignancies

These research directions would advance understanding of both basic cell biology and cancer pathogenesis related to KLHDC8B function .