S100A6 promotes cell proliferation in human nasopharyngeal carcinoma via the p38/MAPK signaling pathway.
We have identified a cDNA whose sequence is preferentially expressed when quiescent fibroblasts are stimulated to proliferate. The steady-state levels of the mRNA corresponding to this clone, called 2A9, are increased by serum, platelet-derived growth factor, and epidermal growth factor, but not by insulin or platelet-poor plasma. mRNA levels of 2A9 are also increased in human acute myeloid leukemia. The 2A9 cDNA has been molecularly cloned from an Okayama-Berg library, and its complete nucleotide sequence has been determined. It has an open reading frame of 270 nucleotides, which has a 55% homology with the coding sequence of the beta-subunit of the S-100 protein, a calcium-binding protein that belongs (like calmodulin and the vitamin D-dependent intestinal calcium-binding protein) to the family of calcium-modulated proteins and is found in abundance in several human tumors, including melanoma. The S-100 protein and the deduced aminoacid sequence of 2A9 are also partially homologous to the small subunit of a protein complex that serves as a cellular substrate to tyrosine kinase. The partial homology of 2A9 (whose RNA is inducible by growth factors and is overexpressed in human acute myeloid leukemias) to the S-100 protein, other calcium-modulated proteins, and the subunit of a substrate for tyrosine kinase, is particularly interesting in view of the role attributed to calcium and tyrosine kinases in the regulation of cell proliferation.