Transcriptional activation by the human Hsp70-associating protein Hap50.
We investigated human Hap50, the large isoform of the previously characterized Hsp70/Hsc70-associating protein Hap46, also called BAG-1, for effects on transcriptional activities. Overproduction by transient transfection led to enhanced expression of reporter gene constructs in various cell types using different promoters, suggesting independence of promoter type. Similarly, overexpression of Hap50 resulted in increased levels of poly(A)(+ )mRNAs in HeLa, COS-7, 3T3 and HTC cells. Concomitantly, the expression of some selected endogenous genes, such as those coding for c-Jun and the glucocorticoid receptor, was enhanced significantly relative to actin. Nuclear runoff transcription assays using HeLa cells showed that the effect is caused by increased transcription rates rather than mRNA stabilization. Activation of transcription by Hap50 occurred at 37 degrees C and did not require prior thermal stress, as is the case for Hap46. In accordance with these biological effects, Hap50 is localized exclusively in the nuclear compartment of different cell types, whereas Hap46 is mostly cytoplasmic in unstressed cells, as revealed by use of fusion constructs with green fluorescent protein. High cellular levels of Hap50 were found to make cells less susceptible to adverse environmental effects such as heat stress. Our data suggest that Hap50 is a nuclear protein that acts in cells to increase the transcription of various genes.
Niyaz
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Y
Ruprecht-Karls-Universität Heidelberg, Biochemie-Zentrum Heidelberg, Biologische Chemie, Im Neuenheimer Feld 501, D-69120 Heidelberg, Germany.
Zeiner
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M
Gehring
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U
D016475:3T3 Cells; D000818:Animals; D019556:COS Cells; D006528:Carcinoma, Hepatocellular; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins; D015870:Gene Expression / Q000502:physiology; D017930:Genes, Reporter; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007536:Isomerism; D008113:Liver Neoplasms; D051379:Mice; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011960:Receptors, Estrogen / Q000235:genetics; D011965:Receptors, Glucocorticoid / Q000235:genetics; D014157:Transcription Factors; D015533:Transcriptional Activation / Q000502:physiology*; D014407:Tumor Cells, Cultured
C091732:BCL2-associated athanogene 1 protein; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D018840:HSP70 Heat-Shock Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D011960:Receptors, Estrogen; D011965:Receptors, Glucocorticoid; D014157:Transcription Factors