Lysosomal Protein Transmembrane 4 Beta (LAPTM4b)

LAPTM4B was overexpressed in hepatocellular carcinoma compared with normal liver tissue, and its expression inversely correlated with the degree of tumor cell differentiation. Overexpression of full-length LAPTM4B increased the efficiency of colony formation in a hepatoma cell line.

The deduced 317-amino acid protein has a calculated molecular mass of 35 kD. It has 4 transmembrane domains, an SH3 domain-binding PxxP motif at both its N and C termini, a conserved lysosome targeting signal at its C terminus, 1 potential N-glycosylation site, 8 putative phosphorylation sites, and 4 N-myristoylation sites. LAPTM4B shares 92% amino acid identity with its mouse homolog and 46% identity with human LAPTM4A.