Identification of a 38-kDa protein (p38) in HL-60 leukemic cells as a truncated actin

Exposure of human leukemic HL-60 cells to monocyte-inducing compounds is accompanied by numerous newly synthesized protein changes in subfractions of the cell. Two proteins with molecular weights of 42,000 and 38,000 (p42, p38), present in the ribosomal salt wash (RSW) of proliferating cells, were markedly elevated and suppressed, in PMA-induced differentiated cells. Actin was identified as a component of p42. P38 cross-reacted with an actin-specific monoclonal antibody in Western blot analysis. Sequencing of gel-purified p38 showed that it was not N-terminally blocked and represented a truncated actin cleaved between val 43 and met 44. The reduction of p38 accompanying proliferating to differentiated cell transition may be indicative of proteolytic differences between the two cellular phenotypes.