Molecular cloning and sequencing of a 58-kDa membrane- and microfilament-associated protein from ascites tumor cell microvilli with sequence similarities to retroviral Gag proteins.
The MAT-C1 subline of the 13762 rat mammary adenocarcinoma has highly stable, branched microvilli and immobile cell surface receptors. A membrane- and microfilament-associated 58-kDa protein (p58) in the MAT-C1 microvilli has been implicated in the stabilization of the microvilli and microfilament-membrane interactions. This protein is associated with a high M(r) glycoprotein complex containing the (proto)oncogene p185neu and other signal transduction components in a putative microfilament-associated signal transduction particle. Amino acid sequences were obtained from two trypsin peptides of p58. Screening a MAT-C1 cDNA library with a degenerate oligonucleotide derived from the larger peptide and polymerase chain reaction amplification of cDNA ends permitted the isolation of overlapping cDNAs encoding the 427-amino acid open reading frame of p58. In vitro transcription and translation using a full-length cDNA gave a protein of approximately 55 kDa, which reacts with anti-p58 antiserum and reconstitutes into a complex with actin and glycoproteins from the membrane-microfilament interaction site. When COS-7 cells were transfected with the full-length cDNA, p58 was localized in a punctate distribution. In addition, the transfected cells exhibited fewer microfilament cables than untransfected neighboring cells. The amino acid sequence showed a surprising similarity to mammalian retroviral Gag proteins and included regions corresponding to p15, p12 and the N-terminal 80% of p30. Comparisons of p58 and the corresponding regions of the Gag proteins for Moloney murine leukemia virus indicated that about 60% of their amino acid residues were identical. These studies suggest that p58 is the product of an endogenous retroviral gene whose expression as a cellular protein alters the properties of the tumor cell to provide a selective advantage for tumor growth in the animal.
Juang
S H
SH
Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Florida 33101.
Huang
J
J
Li
Y
Y
Salas
P J
PJ
Fregien
N
N
Carraway
C A
CA
Carraway
K L
KL
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004279:DNA, Viral; D015683:Gene Products, gag / Q000737:chemistry* / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics*; D008871:Microvilli / Q000378:metabolism; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D051381:Rats; D012190:Retroviridae / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured
D018076:DNA, Complementary; D004279:DNA, Viral; D015683:Gene Products, gag; D008565:Membrane Proteins; D008840:Microfilament Proteins; C500813:membrane and microfilament-associated protein p58, rat