Identification of a mammary transforming gene (MAT1) associated with mouse mammary carcinogenesis.

Abstract

We have developed an eent in vitro transformation system using N-methyl-N-nitrosourea that aflows us to study the role of hormones and growth factors in mouse mammary tumorigenesis. Ulizing this system, we reported earlier that mammary tumors induced in vitro with N-methyl-N-nitrosourea in the presence of mamogenic hormones (progesterone and prolactin) contain predominately an activated c-Ki-ras protooncogene with a G35 --A35 transitional mutation in the 12th codon. Mammary tumors induced in the presence of another mitogen, lithium (Li), do not have a mutation in the c-Ki-ras protooncogene. By using an expression cloning system, a pl d cone containing a 1. transversion mutations at the 61st codon of the H-ras protooncogene (9-12). A majority ofthymic lymphomas induced with MNU, on the other hand, contain a G35 --A35 mutation in the N-ras protooncogene (13,14).The long-term goal of our laboratory is to understand the role of mammogenic hormones and related growth factors in the growth and differentiation of MECs and the manner in which these factors influence the induction of mammary neoplasias of different phenotypes and genotypes. To achieve our goal, during the past several years we have developed a defined serum-free cell culture system in which mouse MECs embedded in a three-dimensional collagen gel matrix can be grown, induced to differentiate, and be neoplastically transformed with chemical carcinogens (15). Using this system, we have observed that the types of mammary lesions induced by carcinogens are greatly influenced by the mitogens present around the time of carcinogen treatment. Earlier we reported on an in vitro system for the induction of preneoplastic hyperplastic alveolar nodules (HANs) and carcinomas from MECs exposed to the direct-acting chemical carcinogen MNU in the presence of different mitogens (16). When mouse MECs were grown in the presence of the mammogenic hormones progesterone and prolactin (PPRL) during MNU administration, the predominant types of lesions induced were a high incidence ofHANs and carcinomas with squamous metaplasia. In contrast, when epidermal growth factor was used as a mitogen during the carcinogen treatment, only a low incidence of ductal hyperplasia was detected, although the extent of MEC proliferation between the two groups was equivalent. The genetic analysis of these lesions indicated that the activation ofthe protooncogene was also dependent on the mitogen used around the time of carcinogen treatment. The majority (80%o) of the HANs and carcinomas induced with MNU in the presence of PPRL had an activation ofthe protooncogene c-Ki-ras by a specific G35 -* A35 point mutation at codon 12. The activation of the protooncogene was determined to be an early event in this carcinogenesis process because the activation was detected in preneoplastic lesions (17). In contrast, activation of c-Kiras was absent in all the ductal hyperplasias induced by MNU in the presence of the mitogen epidermal growth factor. Involvement of the same type of c-Ki-ras mutation ha...

The Death Effector Domain of PEA-15 Is Involved in Its Regulation of Integrin Activation

“…The final 1050 bases of this region are 70% identical to MAT1, a transforming cDNA isolated from a lithium-induced mouse mammary tumor (27). To determine whether the 3Ј-UTR is necessary for the reversal of Ha-Ras integrin suppression, we tested a construct without this sequence and found that it functioned like the full-length cDNA (data not shown).…”

Antitumor effect of E1A in ovarian cancer by cytoplasmic sequestration of activated ERK by PEA15

“…One explanation for this apparent discrepancy could be that the 2.4-kb cDNA for PEA15 contains the entire sequence from the proto-oncogene MAT1, and deregulation of this MAT1 region may contribute to the apparent tumorigenicity of PEA15 (Estelles et al, 1996). MAT1 is known to neoplastically transform NIH3T3 mouse fibroblasts and the mammary epithelial cell line TM3 (Bera et al, 1994). Another study reported that the human homolog of MAT1 (hMAT1) was expressed in the human breast cancer cell lines MDA-MB-231, BT20, and T47D at levels 10 times higher than those in normal human mammary epithelial cells (Hwang et al, 1997); this difference in hMAT1 expression level may be partly responsible for the tumorigenicity of MDA-MB-231 and BT20 cells.…”

The death effector domain protein family

“…PEA-15 contains the mammary transforming (MAT1) proto-oncogene in the 3 0 untranslated region of the 2.5 kb splice form (Bera et al, 1994;Tsukamoto et al, 2000). The MAT1-containing PEA-15 mRNA is expressed weakly during certain physiological circumstances, but becomes strongly expressed in murine mammary tumors and squamous carcinoma cells (Dong et al, 2001).…”