James D. Shull

Expression of the prolactin gene in normal and neoplastic human breast tissues and human mammary cell lines: Promoter usage and alternative mRNA splicing

Prolactin (PRL) has been implicated in the development of mammary cancer in rodents and humans. Although PRL and its mRNA have been detected in breast tissues and some mammary cell lines, the role of PRL as an autocrine/paracrine growth factor within the breast is not clear. A second, more distal, promoter has recently been identified in the human PRL gene. We have used reverse transcription-polymerase chain reaction (RT-PCR) to determine whether the distal or the proximal promoter directs expression of the PRL gene in normal and neoplastic breast tissues and in mammary cell lines. Total RNA was isolated from 10 normal and 20 neoplastic breast tissue samples and from 8 mammary cell lines; MDA-MB-231, SK-BR-3, T-47D, MCF10, MCF10T2, and 3 MCF7 derivatives. The RNA was reverse transcribed to cDNA using random hexamers as primers. PCR amplification of the cDNAs was performed, using a variety of PRL-specific primer pairs, and the DNA products were subjected to agarose gel electrophoresis and Southern blotting. The resulting data indicate that the PRL gene is expressed in the majority of both normal and neoplastic breast tissue samples, as well as all of the mammary cell lines. PRL-specific PCR products corresponding to transcripts that originated from the distal promoter were observed in a subset of the normal and neoplastic breast tissue samples and mammary cell lines. Together these data indicate that PRL transcripts in human breast tissues and human mammary cell lines originate, at least in part, from the distal PRL promoter. In addition, data are presented which suggest that PRL transcripts in breast tissues and mammary cell lines may undergo alternative splicing.

Sequence of the promoter region of the mouse gene encoding ornithine aminotransferase

We have isolated and sequenced the promoter region of the mouse gene (mOAT) encoding ornithine aminotransferase. A comparison of these mOAT sequences with previously reported sequences for the rat and human genes encoding OAT, rOAT and hOAT, respectively, revealed a 256-bp region flanking the transcription start point that is highly conserved between the three genes. This region contains sequence motifs resembling binding sites for general transcription factors, as well as other trans-acting regulatory proteins.

Epidermal growth factor induces prolactin mRNA in GH4C1 cells via a protein synthesis-dependent pathway.

Prolactin (PRL) gene expression is regulated through a complex network of signal transduction pathways activated by various hormones and growth factors. Estrogens regulate PRL gene transcription in vivo through both direct and indirect, protein synthesis-dependent, mechanisms. Therefore, we hypothesized that other stimulators of PRL gene transcription might also act via protein synthesis-dependent mechanisms. To test this hypothesis, we examined, in GH4C1 rat pituitary tumor cells, the effects of protein synthesis inhibitors on the induction of PRL mRNA by known stimulators of PRL gene transcription. Whereas induction by epidermal growth factor (EGF) was abolished by cycloheximide and puromycin, increases in PRL mRNA caused by thyrotropin releasing hormone, 12-O-tetradecanoylphorbol 13-acetate, forskolin, or dibutyryl cyclic AMP were unaffected. These data suggest that the induction of PRL mRNA by EGF may require the induced synthesis of an intermediary regulatory protein.

Dietary lignin, an insoluble fiber, enhanced uterine cancer but did not influence mammary cancer induced by N-methyl-N-nitrosourea in rats

Previous investigations suggested potential breast cancer-preventive properties of dietary fiber from cabbage. The purpose of the present investigation was to determine whether lignin, a component of cabbage fiber, would protect against mammary carcinogenesis by N-methyl-N-nitrosourea (MNU) in Sprague-Dawley rats. A six-week study was conducted using diets containing 0.5-5% dietary wood lignin (a readily available, purified source). These diets were well tolerated by the rats, and a carcinogenesis study using 5 mg MNU/100 g body wt i.v. at 50 days of age was conducted, with the 2.5% lignin diet fed from 6 through 8 weeks of age followed by 5% lignin diet until 20 weeks after MNU. Dietary lignin and MNU treatment increased food consumption (p < 0.05), and body weight was slightly reduced at 10 and 20 weeks after MNU in the MNU-5% lignin diet group (p < 0.05). Serum estradiol was not altered by dietary lignin or MNU treatment, but uterine weights were highest in the MNU-control diet group 4 and 12 weeks after MNU. Expression of creatine kinase B, and estrogen-responsive gene, was lower in eh uteri of the MNU-lignin diet group than in other groups at 20 weeks. Mammary carcinogenesis was not altered by dietary lignin. However, uterine endometrial adenocarcinoma was observed only in the MNU-lignin diet group (4 carcinomas/40 effective rats) (p < 0.05).

The ornithine aminotransferase-encoding gene family of rat: cloning, characterization, and evolutionary relationships between a single expressed gene and three pseudogenes

As a first step towards understanding the molecular mechanisms through which the expression of the gene (OAT) encoding ornithine aminotransferase (OAT) is regulated in a tissue-specific manner, we have used a near full length OAT cDNA to isolate related sequences from a rat genomic DNA library. Twenty-one unique clones representing five contigs and spanning approximately 140 kb of genomic DNA were isolated and characterized. From these clones we have identified a single expressed OAT gene and three processed pseudogenes. The comparison of the EcoRI, BamHI, and HindIII fragments contained within these genomic clones with those detected in total genomic DNA by the cDNA probe suggests that essentially all of the OAT-related sequences in the rat genome have been isolated. Thus, the tissue-specific regulation of OAT gene expression appears to be effected through a single expressed gene. Data are presented which suggest that the OAT-1, OAT-2, and OAT-3 pseudogenes arose approximately 28.5, 7.3, and 25.1 Myr ago, respectively. Mutation rates are presented for each codon position of the expressed rat and human OAT genes. The region of the rat genome flanking the boundary of the OAT-3 pseudogene is of additional interest as it shares considerable identity to sequences contained within expressed genes and flanking other processed pseudogenes.

Transcription of sequences upstream of the rat prolactin gene suggests the existence of a second promoter

The transcription of the rat prolactin gene domain has been examined using a modified Southern blot procedure. Cloned genomic DNAs were resolved by electrophoresis in agarose, transferred to nitrocellulose, and probed with radiolabeled RNA that had been synthesized in vitro by nuclei isolated from pituitary tumor cells. Data presented in this paper illustrate that single copy genomic sequences located within 7.3 kb upstream of exon 1 are transcribed. Single copy or low copy number DNA sequences that reside greater than 7.3 kb upstream of exon 1, or downstream of exon 5 were not transcribed at detectable levels. These data suggest that a second promoter may exist upstream of the rat prolactin gene and that this second promoter may be active in pituitary cells.