LAPTM4B Antibody

What is LAPTM4B and why is it significant in cancer research?

LAPTM4B is a multi-pass membrane protein belonging to the LAPTM4/LAPTM5 transporter family, encoded by a gene located on chromosome 8q22.1 . It functions as an oncogene with critical roles in:

• Tumor cell proliferation and growth regulation in vitro and in vivo

• Invasion and metastasis promotion

• Apoptosis resistance and autophagy initiation

• Drug resistance development

LAPTM4B is upregulated in various human cancers including hepatocellular carcinoma (HCC), breast cancer, gastric cancer, lung cancer, and ovarian carcinoma . In HCC specifically, LAPTM4B promotes cancer stem cell proliferation via the Wnt1/c-Myc/β-catenin pathway . Its upregulation correlates with adverse outcomes in HCC patients but potentially increases sensitivity to PD-L1 monoclonal antibody therapy .

What are the known isoforms of LAPTM4B and their significance?

Research has identified two primary LAPTM4B protein isoforms:

Immunohistochemistry studies confirm that LAPTM4B-35, not LAPTM4B-24, shows significant upregulation across various cancer types . The ratio between these isoforms appears relevant to cancer development, with LAPTM4B-35 expression positively correlating with lymph node metastasis and inversely associated with cancer tissue differentiation and patient survival in gallbladder cancer, extrahepatic cholangiocarcinoma, ovarian cancer, HCC, and gastric cancer .

What are the optimal conditions for LAPTM4B antibody use in Western blot applications?

Based on comprehensive assessment of commercially available antibodies, the following parameters yield optimal results for LAPTM4B detection via Western blot:

Researchers should note that sample-dependent variations exist, necessitating optimization for each experimental system . Both LAPTM4B-35 and LAPTM4B-24 isoforms may be detected, with their relative abundance potentially providing insight into disease progression .

What are the recommended protocols for LAPTM4B immunohistochemistry?

For optimal LAPTM4B detection in tissue sections:

The search results indicate successful LAPTM4B immunohistochemistry across various cancer tissues, particularly in studies examining correlations between expression and clinical outcomes .

How does LAPTM4B contribute to cancer stem cell maintenance in HCC?

LAPTM4B plays a crucial role in maintaining cancer stem cell properties in HCC through several sophisticated mechanisms:

LAPTM4B-YAP Positive Feedback Loop:

• LAPTM4B inhibits ubiquitin-dependent degradation of YAP (Yes-associated protein)

• YAP binds to cAMP responsive element binding protein-1 (CREB1) and promotes LAPTM4B transcription

• This creates a self-amplifying loop that enhances stemness in tumor cells

Experimental evidence demonstrates that:

• Overexpression of LAPTM4B increases CD133+ cell populations (a stemness marker) in HCC cell lines

• LAPTM4B upregulates expression of stemness-associated genes including SOX9, OCT4, NANOG, and the stem cell surface marker EpCAM

• LAPTM4B is regulated by ETV1 (a transcription factor) specifically in liver cancer stem cells

The LAPTM4B influence on liver cancer stem cells is mediated via the Wnt1/c-Myc/β-catenin pathway, which is critical for stem cell maintenance . These findings suggest LAPTM4B as a potential therapeutic target to address the stem cell-like properties contributing to treatment resistance, recurrence, and metastasis.

What mechanisms explain LAPTM4B's role in chemotherapy resistance?

LAPTM4B contributes to chemotherapy resistance through several distinct cellular mechanisms:

Ceramide Compartmentalization:

• High LAPTM4B expression increases ceramide clearance from late endosomes, potentially sensitizing cells to ceramide-induced apoptosis

• Low LAPTM4B expression causes ceramide sequestration in late endosomes, protecting cells from ceramide toxicity while sensitizing them to lysosome-mediated death

Autophagy Modulation:

• LAPTM4B activates ATG3 transcription to regulate HCC cell apoptosis and autophagy

• Under starvation conditions, LAPTM4B facilitates cell survival, inhibits apoptosis, and induces autophagic flux

• This autophagy-promoting effect may help cancer cells survive during chemotherapy

EGFR Degradation Prevention:

• LAPTM4B blocks EGF-stimulated EGFR intraluminal sorting and degradation

• By preventing EGFR degradation, LAPTM4B sustains pro-survival signals even during chemotherapy

The complex interaction between LAPTM4B expression levels and these cellular processes suggests that targeting LAPTM4B could be a strategy to overcome chemoresistance in cancer treatment.

How does LAPTM4B interact with the immune system in tumor microenvironments?

LAPTM4B has significant and complex interactions with the tumor immune microenvironment:

Immune Cell Infiltration Patterns:
In Ph+ B-ALL, high LAPTM4B expression correlates with specific immune cell profiles:

Immune Checkpoint Regulation:

• LAPTM4B expression positively correlates with CTLA4, HLA-E, and ICOS expression

• LAPTM4B negatively correlates with TNFRSF14 expression

Cytokine/Chemokine Effects:

• CXCL8 secretion by LAPTM4B drives myeloid-derived suppressor cell (MDSC) migration

• High LAPTM4B expression correlates with lower expression of several chemokines, including CCL1, CCL11, CCL15, CCL19, CCL21, CCL22, CCL24, and CCL25

Immunotherapy Implications:

• LAPTM4B affects PD-L1 receptor expression in the tumor microenvironment

• It enhances tumor suppression induced by PD-L1 monoclonal antibodies in HCC patients

These findings suggest that LAPTM4B expression status could potentially predict immunotherapy response and serve as a complementary therapeutic target in cancer treatment strategies.

What are effective experimental approaches for LAPTM4B knockdown studies?

Based on published research methodologies, these approaches have proven successful for LAPTM4B functional studies:

Knockdown Systems:

• Lentiviral-mediated silencing has successfully reduced LAPTM4B levels by >3-fold at both mRNA and protein levels

• Stable knockdown models can be generated in cancer cell lines like SMMC-7721

Validation Approaches:

• Flow cytometry to assess effects on CD133+ stem cell populations

• Western blotting to confirm protein level reduction

• qRT-PCR to verify transcript reduction

• Analysis of downstream effects on stemness-associated genes (SOX9, OCT4, NANOG, EpCAM)

In Vivo Validation:

• Xenograft models in nude mice have demonstrated that LAPTM4B knockdown significantly reduces tumor size compared to control cells

• Conversely, tumors formed from LAPTM4B-upregulated xenografts show significantly increased growth

Cell Models:

• HCC cell lines like SMMC-7721 (high endogenous LAPTM4B) and PLC/PRF/5 (lower LAPTM4B expression) provide useful comparative models

• CD133+ tumor cells from HepG2 or Huh7 HCC cell lines effectively simulate stem-like tumor cells for studying LAPTM4B functions

How can researchers effectively differentiate between LAPTM4B isoforms in experimental studies?

Researchers can effectively differentiate between LAPTM4B isoforms using these approaches:

Western Blot Analysis:

• LAPTM4B-35 appears at approximately 35 kDa

• LAPTM4B-24 appears at approximately 24 kDa

• Both forms can be detected with appropriate antibodies, though specific isoform-selective antibodies may be required for clearer distinction

Expression Ratio Analysis:

• Quantitative analysis of both isoforms can provide insights into their ratio, which appears relevant to cancer development

• Calculating the LAPTM4B-35 to LAPTM4B-24 ratio may serve as a prognostic indicator

Post-Translational Modification Analysis:

• Analysis of specific modifications can help distinguish isoforms:

  • K93 ubiquitination site

  • Y233 and Y314 phosphorylation sites

Functional Overexpression Studies:

• Selective overexpression of each isoform can help determine their distinct roles

• LAPTM4B-35 appears to be the primary oncogenic form and should be the focus for cancer studies

What are the emerging research areas for LAPTM4B in cancer therapeutics?

Several promising research directions have emerged:

Immunotherapy Combinations:

• LAPTM4B expression correlates with PD-L1 response and affects the tumor immune microenvironment

• Studies suggest LAPTM4B could be a biomarker for immunotherapy response

• Investigating combined targeting of LAPTM4B and immune checkpoints represents a promising therapeutic approach

Cancer Stem Cell Targeting:

• The LAPTM4B-YAP feedback loop in cancer stem cells presents a potential therapeutic target

• Disrupting this loop could reduce stemness and improve treatment outcomes

Biomarker Development:

• LAPTM4B expression levels could serve as prognostic indicators

• The ratio of LAPTM4B isoforms might provide additional prognostic information

Drug Resistance Mechanisms:

• Further understanding of how LAPTM4B mediates drug resistance could lead to strategies to overcome treatment failures

• The ceramide compartmentalization function of LAPTM4B presents a potential target for enhancing chemotherapy efficacy