May be involved in cell adhesion and cell matrix association. May play a role in the regulation of anchorage versus migration or proliferation versus differentiation via its phosphorylation. May be a novel marker for leukemia diagnosis and for immature hematopoietic stem cell subsets. Belongs to the tetraspanin web involved in tumor progression and metastasis. Interacts with CDH2/N-cadherin, CDH3/P-cadherin, SDC1/syndecan-1, SDC4/syndecan-4 and the serine protease ST14/MT-SP1. Also interacts with SRC and PRKCG/protein kinase C gamma. Shedding may also lead to a soluble peptide. Highly expressed in mitotic cells with low expression during interphase. Detected at highest levels in skeletal muscle and colon with lower levels in kidney, small intestine, placenta and lung. Up-regulated in a number of human tumor cell lines, as well as in colorectal cancer, breast carcinoma and lung cancer. Also expressed in cells with phenotypes reminiscent of mesenchymal stem cells and neural stem cells. Phosphorylated on tyrosine by kinases of the SRC family such as SRC and YES as well as by the protein kinase C gamma/PRKCG. Dephosphorylated by phosphotyrosine phosphatases. Also phosphorylated by suramin, a heparin analog. Tyrosine phosphorylated in response to dissociation of integrin alpha-6 beta-4 from laminin-5. N-glycosylated. A soluble form may also be produced by proteolytic cleavage at the cell surface (shedding). Another peptide of 80 kDa (p80) is present in cultured keratinocytes probably due to tryptic cleavage at an unidentified site on its N-terminal side. Converted to p80 by plasmin, a trypsin-like protease. Truncated N-terminus.