Regulation of hsc70 expression in the human histiocytic lymphoma cell line, U937

The transcription of hsc70, a cognate member of the hsp70 gene family, is suppressed in the terminally differentiated human histiocytic lymphoma cell line, U937, and appears to be regulated in the absence of heat shock. We have examined the 5' upstream regulatory region of 450 bp which contains a putative regulatory sequence of 18 bp in addition to known cis-elements such as HSEs, CCAAT boxes, Sp1 binding sites and AP2 binding sites. The 18 bp cis-element formed larger complexes with nuclear localized transfactors when extracts were prepared from differentiated rather than from proliferating cells. These larger complexes were also detected in nuclear extracts of serum-deprived cells, suggestng that such complexes may be related to the suppression of hsc70 gene transcription in Go arrested cells. The level of HSC70 protein as determined using monoclonal antibodies, increased threefold in differentiated cells. The apparent discrepancy between the levels of hsc70 mRNA and HSC70 protein can be explained by a rapid turnover of HSC70 in proliferating cells.