Identification of nuclear proteins encoded by viral and cellular myc oncogenes

Abstract

The myelocytomatosis viruses are a family of replication-defective avian retroviruses that cause a variety of tumours in chickens and transform both fibroblasts and macrophages in culture through the activity of their oncogene v-myc. A closely related gene (c-myc) is found in vertebrate animals and is thought to be the progenitor of v-myc. Changes in the expression and perhaps the structure of c-myc have been implicated in the genesis of avian, murine and human tumours (for a review, see ref. 15). Elucidation of the mechanisms by which v-myc and c-myc might elicit tumorigenesis requires identification of the proteins encoded by these genes. To this end, we have expressed a portion of v-myc in a bacterial host and used the resulting protein to raise antisera that react with myc proteins. We report here that v-myc and c-myc encode closely related proteins with molecular weights (MWs) of approximately 58,000. Integration of retroviral DNA near or within c-myc in avian lymphomas apparently enhances expression of the gene. Here we have used cells from one such tumour to identify the protein encoded by c-myc and find that the coding domain for the gene is probably intact.

V-myc in a simple, single gene retroviral vector causes rapid induction of leukemia and concomitant apoptosis following bone marrow transplantation

“…v-myc cDNA 16 or a ␥-actin promoterdriven v-myc expression cassette was inserted into the HindIII/EcoRI site of LK to generate new vectors, termed Lvmyc2 and LNAv-myc, respectively ( Figure 1). pLK, pLv-myc2 or pLNAv-myc DNA was introduced into the ⌿ packaging line 17 by calcium phosphate precipitation together with pMolNeo DNA 1 at a ratio of 20:1 (w/w) followed by selection in 500 g/ml G418.…”

“…The relative viral titers produced by individual clones were examined by viral RNA-blot analysis and probing with 32 P-labelled v-myc-specific cDNA probe. 16 The clones of apparent highest titer were further examined by analyzing their ability to transform Rat-1 cells in vitro. 1 The ⌿2AV viral…”

“…pLNAv-myc (c) and pLvmyc2 (d) were produced by the insertion of a ␥-actin promoter driven v-myc expression cassette or a 1.7 kb v-myc fragment from MC29 into pLK, respectively. 16 Shaded boxes, LTRs, ⌿ + packaging region; thick vertical line, viral splice donor site.…”

“…The resultant vector is 4.7 kb and contains a multiple cloning site and all features of LNL6 except the neo gene and the following sequences between neo and the HindIII site: FCV (env C) pol region, some unknown intervening sequence of approximately 20 bp and part of the mos sequence of MSV (Genebank LNL6 sequence). Lv-myc-2 was constructed by the insertion of HindIII/XhoI 1.7 kb v-myc cDNA fragment derived from PAB 16 into HindIII linearized LK (Figure 1). …”

A critical appraisal of the immunohistochemical detection of the c-myc oncogene product in colorectal cancer

“…The c-myc oncogene encodes for a 62,000 molecular weight protein product, p62c-mYc (Alitalo et al, 1983;Hann & Eisenman, 1984), which is predominantly located in the nucleus (Eisenman et al, 1985;Evan & Hancock, 1985) and thought to be involved in the regulation of cellular proliferation. A definitive role for the oncoprotein has not been elucidated; however, the cellular homologues of the c-myc gene are highly conserved across species suggesting that it is of considerable functional importance.…”