Expressions and Alterations of LAPTM4B in Human Cancers
In order to examine the expression profile of LAPTM4B in pan-cancers, we evaluated its expression across 34 cancer types using data from TCGA, TARGET, and GTEx databases. Our findings revealed high LAPTM4B expression in 28 cancer types compared to normal tissues, including glioblastoma (GBM), lower-grade glioma (LGG), uterine corpus endometrial carcinoma (UCEC), breast invasive carcinoma (BRCA), cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), lung adenocarcinoma (LUAD), esophageal carcinoma (ESCA), stomach and esophageal carcinoma (STES), colon adenocarcinoma (COAD), colon adenocarcinoma/Rectum adenocarcinoma esophageal carcinoma (COADREAD), stomach adenocarcinoma (STAD), head and neck squamous cell carcinoma (HNSC), lung squamous cell carcinoma (LUSC), liver hepatocellular carcinoma (LIHC), high-risk Wilms tumor (WT), skin cutaneous melanoma (SKCM), bladder urothelial carcinoma (BLCA), thyroid carcinoma (THCA), rectum adenocarcinoma (READ), ovarian serous cystadenocarcinoma (OV), pancreatic adenocarcinoma (PAAD), testicular germ cell tumors (TGCT), uterine carcinosarcoma (UCS), acute lymphoblastic leukemia (ALL), acute myeloid leukemia (LAML), Adrenocortical carcinoma (ACC), and cholangiocarcinoma (CHOL). While, low LAPTM4B expression was observed in 4 cancer types, Pan-kidney cohort (KIPAN), prostate adenocarcinoma (PRAD), kidney renal clear cell carcinoma (KIRC), and kidney chromophobe (KICH) (Fig. 1A). Specifically, LAPTM4B exhibited high expression in BLCA, BRCA, CHOL, COAD, ESCA, HNSC, LIHC, LUAD, LUSC, READ, STAD, and UCEC, while showing low expression in KICH, KIRC, PRAD, and THCA compared to adjacent paired normal tissues (Fig. 1B). These results suggest that elevated LAPTM4B expression is associated with cancer progression in a majority of cases.
The amplification of LAPTM4B was observed most frequently in UCS, BRCA, BLCA, OV, PRAD, and LIHC, (Fig. 1C), and common in most cancers (Fig. 1C, D). Moreover, we found 34 mutation sites between amino acids 0 and 317, including 24 missense mutations, 2 truncating, 8 SV/fusion, and S265N as the most frequent mutation sites within LAPTM4B across cancers (Fig. 1E, F).
To elucidate potential associations between LAPTM4B and intracellular epigenetic alterations, we examined the status of genomic methylation and the expression of genes involved in mRNA methylation in various types of cancer cells using data from cBioPortal database. We found that there were significant negative correlations between LAPTM4B expression and gene promotor methylation in most tumors (Supplementary Fig. 1A). Increased methylation of LAPTM4B mRNA was related to poorer OS in patients with GBM and LGG (Supplementary Figure 1B, C). Furthermore, the relationships between LAPTM4B and genes involved in mRNA m1A, m5C, m6A modifications were evaluated. LAPTM4B expression was significantly positively related to these RNA modification genes in almost all tumors (Supplementary Figure 1D). These results indicated that LAPTM4B could influence tumor development by regulating the repair of RNA and DNA methylation in cancers.
The Clinical Features associated with LAPTM4B alterations in Pan-cancers
To evaluate the clinical significance of elevated LAPTM4B expression in various cancers, we conducted a Cox proportional hazards model analysis encompassing OS, DSS, DFI, and PFI. Univariate Cox regression analysis of OS, DSS, PFI, and DFI revealed that LAPTM4B served as a significant risk factor for patients in multiple cancer types, including LIHC, B-ALL, SARC, GBMLGG, SKCM, AML, ACC, UVM, CESC, HNSC, KICH, MESO, UVM, BRCA, and PCPG (Fig. 2A). Additionally, Kaplan‒Meier survival analyses of OS, DSS, and PFI were further explored across cancers (Fig. 2B-D).
The performance of the gene signature for diagnostic accuracy was evaluated by the ROC curves. Figure 3 showed that 17 types of cancer had high diagnostic accuracy (AUC > 0.9), including CHOL, ESCA, GBM, HNSC, LAML, LGG, LUAD, LUSC, OV, PAAD, READ, SKCM, STAD, TGCT, THYM, UCEC and UCS. These results suggested that LAPTM4B had good diagnostic value in a variety of cancers. The detailed results of all cancers were exhibited in the Supplementary table 1.
To assess the potential correlation between elevated LAPTM4B expression and the drug response of tumor cells, we conducted Spearman correlation coefficient analysis using data from the GDSC dataset. Our findings revealed increased LAPTM4B expression had increased IC50 values of 14 compounds, including rTRAIL, B-Raf inhibitors (PLX-4720, dabrafenib, SB590885), FTI-277 (FTase inhibitor), bexarotene (RXR agonist), dactolisib (PI3K/mTOR inhibitor), luminespib (HSP90 inhibitor), palbociclib (CDK4/6 inhibitor), (5Z)-7-Oxozeaenol (TAK1 inhibitor), QS11 (ARFGAP1 inhibitor), among others, which suggested that increased LAPTM4B lead drug resistance. Conversely, a negative association was observed with elesclomol and afatinib (EGFR/HER2 inhibitor) responses (Table 1). These results suggest that increased LAPTM4B expression may confer resistance to a broad spectrum of therapeutic agents in tumor cells. Moreover, we also found that LAPTM4B was positively correlated with RNAss and DNAss across most of the cancers (Supplementary Fig. 2A-B), which indicates that high expression of LAPTM4B might be associated with cancer tumor recurrence and metastasis.
Immune Status Analysis of LAPTM4B in Pan-Cancer
To explore the relationship between LAPTM4B expression and immune status in pan-cancer, we conducted a correlation analysis. Overall, we found that LAPTM4B expression was associated with immune subtypes in 19 cancer types and correlated with molecular subtypes in 14 cancer types (Supplementary Fig. 3A-B). Additionally, we analyzed stromal and immune cell scores to investigate the relationship between LAPTM4B expression and the tumor immune microenvironment (TIME) across cancers. We observed a positive correlation between LAPTM4B expression and StromalScore, ImmuneScore, and ESTIMATEScore in PAAD, OV, and UVM (Fig. 4A). While, LAPTM4B expression showed a negative correlation with these scores in GBM, LGG, LAML, BRCA, CESC, LUAD, STES, SARC, KIRP, KIPAN, STAD, LUSC, WT, SKCM, SKCM-M, THCA, NB, and TCGT (Fig. 4A). To explore the correlation between LAPTM4B expression and immune cells, we developed a heat map of LAPTM4B with immune cells by CIBERSORT and xCell. Our result revealed that LAPTM4B was associated with CD8+ T cells, macrophages M2 and Tregs in many cancers, which suggested that high LAPTM4B expression had inhibitory immune microenvironment (Fig. 4B-C). Overall, our findings suggested that elevated LAPTM4B expression might be associated with a potential decrease in patients' immune anti-tumor capabilities.
To investigate whether LAPTM4B expression levels are associated with TMB, MSI, and tumor purity, we conducted analyses using Spearman correlation analysis. The results showed that LAPTM4B expression was positively correlated with TMB in ACC, BRCA, GBMLGG, LAML, LGG, LUAD, PAAD, and THYM, while exhibiting a negative correlation in COAD, COADREAD, ESCA, PRAD, SKCM, and THCA (Fig. 5A). The MSI analysis revealed a positive correlation of LAPTM4B expression with MSI in KIPAN, TGCT, and UVM, while a negative correlation in COAD, COADREAD, DLBC, GBMLGG, LGG, PAAD, PRAD, and THCA (Fig. 5A). Additionally, LAPTM4B showed a significant correlation with tumor purity, with positive associations in CESC, ESCA, GBM, GBMLGG, HNSC, KIPAN, KIRP, LGG, LUAD, LUSC, SARC, SKCM, STAD, STES, TGCT, and THYM, and negative associations in BLCA, LIHC, OV, PCPG, PRAD, UCS, and UVM (Figs. 5A). These findings suggest that LAPTM4B expression might serve as a potential biomarker for immunotherapy.
Subsequently, the correlations of expression levels between LAPTM4B and immune checkpoint genes and immune regulatory genes in cancers were also investigated. We found that LAPTM4B expression was positively related to immune regulatory genes in majority tumor types, especially in PRAD, UVM, THYM, LIHC, BLCA, and OV. While, LAPTM4B expression was negatively related to immune regulatory genes in TGCT, GBM, LUAD, SARC, KIPAN, and SKCM (Fig. 5B). Additionally, LAPTM4B expression was positively related to immune checkpoint genes in most types of tumors, except for some tumors, which were mainly TGCT, GBM, SKCM, and SARC (Fig. 5C). In general, these results suggested that LAPTM4B might regulate immune cell infiltration and immune-related genes functions in most tumor types.
Single-cell and Enrichment Analysis of LAPTM4B Expression in Leukemia
To specifically and deeply depict the pictures of LAPTM4B involving in malignancies, then we focused on hematological malignancies, particularly Ph+ B-ALL, to elucidate and clarify the biological functional characteristics of LAPTM4B in tumors. Taking the advantages of single-cell sequencing and open public data, we found that LAPTM4B was expressed mainly in normal HSCs, progenitors, and AML cells (Fig. 6A-B). In an ALL sample, we found that LAPTM4B was highly expressed in proerythroblasts, but not malignant cells (Fig. 6C-D). Interesting, an analysis based on an expression profiling of 191 B-ALL samples and 3 normal pre-B samples showed that LAPTM4B was more highly expressed in BCR/ABL B-ALL than other subtypes (Fig. 6E). Then, we performed the analysis of the function and pathways of LAPTM4B-related genes in Ph+ B-ALL. We found that genes associated with HSCs and leukemia stem cells (LSCs) were up-enriched in high LAPTM4B expression samples (Fig. 6F-G), as well as genes associated with cell cycle, DNA replication, MYC target, E2F and G2M checkpoint pathways were also up-enriched in in Ph+ B-ALL (Fig. 6H-I).
LAPTM4B deletion impairs the development and progression of Ph+ B-ALL
To instigate the involvement of LAPTM4B in the development of Ph+ B-ALL, we employed a Ph+ B-ALL mouse model. Bone marrow (BM) cells from wild type (WT) or LAPTM4B−/− mice were transfected with retrovirus containing BCR/ABL and then injected into lethally irradicated recipients (Fig. 7A). Overall, the survival time of recipients receiving LAPTM4B−/− BM cells was significantly longer than that receiving WT BM cells (Fig. 7B). We also monitored the number of leukemic cells with BCR/ABL (represented with GFP and B220) in peripheral blood of mice receiving BCR/ABL-transduced WT or LAPTM4B−/− BM cells on the day 10, 20 and 30 post-BM transplantation. We found that the percentages of B-lymphoid leukemic cells were significantly lower in mice receiving BCR/ABL-transduced WT or LAPTM4B−/− BM cells than in those receiving BCR/ABL-transduced WT BM cells at all time points measured (Fig. 7C). To investigate the role of LAPTM4B in BCR/ABL-induced leukemogenesis, we conducted an in vitro assay for proliferation of BCR/ABL transformed BM B-lymphoid progenitors, as described in methods. BCR-ABL-transformed B-lymphoid progenitors from LAPTM4B−/− BM cells exhibited much lower number than it transformed those from WT BM cells (Fig. 7D). Further, in vitro Brdu assays for cell proliferation rate showed that LAPTM4B deletion impaired Ph+ B-ALL cell proliferation and caused G0/G1 arrest (Fig. 7E). These findings demonstrated that LAPTM4B deletion significantly impaired the development and progression of Ph+ B-ALL.
Relationships between LAPTM4B Expression and Immune Status in Ph+ B-ALL
To evaluate the association of LAPTM4B expression with TME in Ph+ B-ALL, we conducted an ESTIMATE analysis to calculate the stromal score, immune score, ESTIMATE score, and tumor purity within Ph+ B-ALL. We found that LAPTM4B expression was not significantly associated with TME in Ph+ B-ALL (Supplementary Fig. 4). Then, the relationship between LAPTM4B and immune cells in Ph+ B-ALL was conducted using xCell algorithm method. The scores of CD4+ memory T cells, CD8+ T cells, HSC, preadipocytes, and Tgd cells were higher; while, the scores of CD4+ Tem, eosinophils, epithelial cells, MSC, and NKT were significantly lower in the high LAPTM4B expression patient samples (Fig. 8A). LAPTM4B expression was negatively related to macrophages M2, NKT, mv endothelial cells, and CD4+ Tem; while they were positively correlated with CD4+ memory T cells, Th2 cells, Tgd cells, CD4+ T cells and microenvironment Score (Fig. 8B). Moreover, immune infiltration scores of tumor-infiltrating lymphocytes (TILs) type in different LAPTM4B expression groups were also evaluated using ssGSEA. The central memory CD4 T cells, effector memory CD4 T cells, immature B cells, plasmacytoid dendritic cells, and immature dendritic cells were highly expressed in the high LAPTM4B expression patient samples (Fig. 8C).
The correlation between LAPTM4B expression and immune-related genes was also assessed. As previous reports, there were 79 genes related to immune checkpoint (Hu et al., 2021). We found that TNFRSF14 and TNFSF14 were lowly expressed in the high LAPTM4B expression samples (Supplementary Fig. 5A). Additionally, TNFRSF14 was negatively correlated with LAPTM4B expression; whereas, CTLA4, HLA-E, and ICOS were positively associated with LAPTM4B expression (Supplementary Fig. 5B). Moreover, the correlation between LAPTM4B and the chemokine genes was also evaluated. We found that CCL1, CCL11, CCL15, CCL19, CCL21, CCL22, CCL24 and CCL25 were lowly expressed in high LAPTM4B expression samples (Supplementary Fig. 5C). But, no significant difference was observed on immunoinhibitory genes, immunostimulatory genes, receptor genes, and MHC genes except for IL6, LTA, ULBP1, and XCR1 (Supplementary Fig. 6A-D). These results suggested that the high expression of LAPTM4B might affected immune microenvironment in Ph+ B-ALL.