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Truncation of Sp1 transcription factor by myeloblastin in undifferentiated HL60 cells
Author(s) -
Rao Jia,
Zhang Fan,
Donnelly Robert J.,
Spector Neil L.,
Studzinski George P.
Publication year - 1998
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/(sici)1097-4652(199805)175:2<121::aid-jcp1>3.0.co;2-q
Subject(s) - sp1 transcription factor , hl60 , biology , microbiology and biotechnology , transcription factor , cellular differentiation , transcription (linguistics) , gene expression , promoter , cell culture , gene , genetics , linguistics , philosophy
When HL60 cells are exposed to 1,25‐dihydroxyvitamin D 3 (1,25D 3 ), they undergo changes approximating the phenotype of the monocyte. Little is known, however, about the regulation and the mechanisms of this transition. It was previously noted that DNA binding by the Sp1 transcription factor in nuclear extracts of HL60 cells is profoundly altered when these cells are induced to differentiate by 1,25D 3 . In the present study, we show that in untreated HL60 cells only a truncated, approximately 30‐kDa Sp1 fragment, encompassing the C‐terminal region, binds to the GC element‐containing DNA. Full‐length 105‐kDa Sp1 protein cannot be detected in these cells, although reverse transriptase–polymerase chain reaction reveals the presence of both 5′ and 3′ ends of Sp1 mRNA. Following treatment with 10 −7 M 1,25D 3 for 96 hr or in cells made resistant to 1,25D 3 or to 1‐β‐D‐arabinocytosine, the Sp1 protein can be demonstrated. After an exposure to purified myeloblastin, a serine protease, purified recombinant Sp1 protein and extracts of 1,25D 3 ‐treated cells show a pattern of DNA binding similar to the pattern seen using extracts of untreated HL60 cells, indicating that the Sp1 protein is a target for myeloblastin. Because myeloblastin is present in naive HL60 cells and is downregulated during their differentiation, inhibition of proteolysis of these transcription factors seems to provide a mechanism through which differentiating HL60 cells can acquire a new repertoire of gene expression, perhaps for the maintenance of the differentiated phenotype. J. Cell. Physiol. 175:121–128, 1998. © 1998 Wiley‐Liss, Inc.