REGULATION OF HSC70 EXPRESSION IN THE HUMAN HISTIOCYTIC LYMPHOMA CELL-LINE, U937

The transcription of hsc7O, a cognate member of the hsp70 gene family, is suppressed in the terminally differentiated human histiocytic lymp homa cell line, U937, and appears to be regulated in the absence of he at 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 A P2 binding sites. The 18 bp cis-element formed larger complexes with n uclear localized transfactors when extracts were prepared from differe ntiated rather than from proliferating cells. These larger complexes w ere also detected in nuclear extracts of serum-deprived cells, suggest ing that such complexes may be related to the suppression of hsc70 gen e transcription in Go arrested cells. The level of HSC70 protein as de termined using monoclonal antibodies, increased threefold in different iated cells. The apparent discrepancy between the levels of hsc70 mRNA and HSC70 protein can be explained by a rapid turnover of HSC70 in pr oliferating cells.