Molecular cloning and characterization of LAPTM4B, a novel gene upregulated in hepatocellular carcinoma

Abstract

Lysosomal-associated protein transmembrane-4 beta (LAPTM4B), a novel gene upregulated in hepatocellular carcinoma (HCC), was cloned using fluorescence differential display, RACE, and RT-PCR. It contains seven exons and encodes a 35-kDa protein with four putative transmembrane regions. Both the N-and C-termini of the protein are proline-rich, and may serve as potential ligands for the SH3 domain. Immunohistochemical analysis localized the protein predominantly to intracellular membranes. Northern blot showed that the LAPTM4B mRNAs were remarkably upregulated in HCC (87.3%) and correlated inversely with differentiation status. LAPTM4B was also overexpressed in many HCC-derived cell lines. It was also highly expressed in fetal livers and certain adult normal tissues including the heart, skeletal muscle, testis, and ovary. Promoter function assays showed a distinct difference in the gene's activities between BEL7402 and HLE cell lines, suggesting that the transcription factors responsible for regulation of the gene in the two cell lines are different, and that possible negative regulatory cis-elements may exist upstream of the promoter region. It was demonstrated that the N-terminus of LAPTM4B was essential for survival of the cells. Cells harboring the full-length LAPTM4B cDNA expression clone displayed a slightly increased efficiency in colony formation. These results suggest that LAPTM4B is a potential protooncogene, whose overexpression is involved in carcinogenesis and progression of HCC. In normal cells, it may also play important roles such as regulation of cell proliferation and survival.

CIK cells from patients with HCC possess strong cytotoxicity to multidrug-resistant cell line Bel-7402/R

“…They found that despite high cytotoxic activity of CIK against lymphoma cells, they had little toxicity against a subset of normal human hematopoietic progenitor cells. Some difference between Bel-7402 and L-02 has been reported recently by Shao et al [26] , that LAPTM4B, a newly found HCC related antigen, was expressed in Bel-7402 but not in L-02. A polyclonal antibody against LAPTM4b has been produced.…”

Differential gene expression in pituitary adenomas by oligonucleotide array analysis

“…Several studies indicate that LAPTM4B plays an important role in tumourigenesis (13,14,19), although its exact mechanism of action remains to be elucidated. The over-expression in ACTH-secreting tumours demonstrated by the microarray analysis and confirmed with the RQ-PCR analysis of grouped tumours may relate to the abundant lysosomes present in corticotroph adenomas (20).…”

Emerging roles of PtdIns(4,5)P2 – beyond the plasma membrane

“…LAPTM4B is a member of the mammalian LAPTM family that comprises LAPTM4A, LAPTM4B and LAPTM5 (Adra et al, 1996;Hogue et al, 2002;Shao et al, 2003). All LAPTM family members are small multitransmembrane proteins that, when overexpressed, are targeted to the late endosome and/or lysosome (Hogue et al, 2002;Milkereit and Rotin, 2011;Pak et al, 2006;Shao et al, 2003;Vergarajauregui et al, 2011); however, endogenous LAPTM4B is localized to both early and late endosomes (Tan et al, 2015a). LAPTM4B is an oncoprotein that is overexpressed in numerous human cancers of undefined oncogenic mechanisms (Kasper et al, 2005).…”