Structure of pp32, an acidic nuclear protein which inhibits oncogene-induced formation of transformed foci.
pp32 is a nuclear protein found highly expressed in normal tissues in those cells capable of self-renewal and in neoplastic cells. We report the cloning of cDNAs encoding human and murine pp32. The clones encode a 28.6-kDa protein; approximately two-thirds of the N-terminal predicts an amphipathic alpha helix containing two possible nuclear localization signals and a potential leucine zipper motif. The C-terminal third is exceptionally acidic, comprised of approximately 70% aspartic and glutamic acid residues; the predicted pI of human pp32 is 3.81. Human and murine pp32 cDNAs are 88% identical; the predicted proteins are 89% identical and 95% similar. Although the structure of pp32 is suggestive of a transcription factor, pp32 did not significantly modulate transcription of a reporter construct when fused to the Gal4 DNA-binding domain. In contrast, in cotransfection experiments, pp32 inhibited the ability of a broad assortment of oncogene pairs to transform rat embryo fibroblasts, including ras + myc, ras + jun, ras + E1a, ras + mutant p53, and E6 + E7. In related experiments, pp32 inhibited the ability of Rat 1a-myc cells to grow in soft agar, whereas it failed to affect ras-induced focus formation in NIH3T3 cells. These results suggest that pp32 may play a key role in self-renewing cell populations where it may act in the nucleus to limit their sensitivity to transformation.
Chen
T H
TH
Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Brody
J R
JR
Romantsev
F E
FE
Yu
J G
JG
Kayler
A E
AE
Voneiff
E
E
Kuhajda
F P
FP
Pasternack
G R
GR
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D018076:DNA, Complementary; D015870:Gene Expression; D005786:Gene Expression Regulation; D016259:Genes, myc; D011905:Genes, ras; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics*; D009857:Oncogenes; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics; D012333:RNA, Messenger; D051381:Rats; D014158:Transcription, Genetic; D014170:Transformation, Genetic; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D009687:Nuclear Proteins; D010750:Phosphoproteins; D012333:RNA, Messenger