Mutation analysis and characterization of HSD17B2 sequence variants in breast cancer cases from French Canadian families with high risk of breast and ovarian cancer.

Estrogen exposure is a risk factor for breast cancer. Given that HSD17B2 gene encodes an enzyme that catalyses estradiol inactivation, it appears as a good candidate breast cancer susceptibility gene. This study was designed to screen for HSD17B2 germline mutations potentially involved in breast cancer predisposition. Our re-sequencing analysis did not identify any deleterious germline mutations, and therefore mutations in HSD17B2 do not explain the clustering of breast cancer cases in non-BRCA1/2 high-risk French Canadian families. However, six sequence variants were identified, including two novel missense variants. Expression assays revealed that p.Ala111Asp and p.Gly160Arg did not alter the catalytic properties of 17beta-hydroxysteroid dehydrogenase type 2 enzyme, although p.Ala111Asp appears to affect protein stability resulting in significant decreases in the protein levels, providing valuable information on structure-function relationship.

Local over-expression of prolactin in differentiating mouse mammary gland induces functional defects and benign lesions, but no carcinoma.

Experimental, clinical, and epidemiological data support the growth-promoting role of endocrine prolactin (PRL) in mammary tumors. PRL is also produced by the breast, where it is now recognized to act as a growth/survival factor via autocrine/paracrine mechanisms. Recent transgenic (Tg) mouse models have revealed the pro-oncogenic effect of PRL over-expression in virgin mammary glands. To address the question whether PRL tumorigenicity was maintained on differentiated mammary glands, we generated mammary-specific Tg mice expressing human (h)PRL under the control of the milk whey acidic protein promoter, which directs autocrine hPRL over-expression in late gestation throughout lactation. Minimal levels of transgene expression were detected in the mammary glands of virgin animals, which at best induced partial ductal branching and lobulo-alveolar structures in older nulliparous females. As expected, expression of mammary hPRL dramatically increased at the end of first pregnancy, and from this point it never returned to baseline, although it peaked at each gestation/lactation cycle. Over-expression of hPRL that starts when the gland is already well into the differentiation process led to various morphological mammary alterations, including abnormally differentiated epithelium, atropy of the myoepithelial layer, dilated ducts, cysts, and lymphocytic infiltrates. These phenotypes tended to worsen with successive pregnancies, also reflecting cumulative damage of failure of involution. Although some older, multiparous females developed benign tumors (papillomas and metaplasias), none of the animals studied developed mammary carcinomas. In addition, we noticed that half of the Tg females exhibited lactation defects, leading to significantly increased pup mortality. This phenotype was due neither to failure of milk production nor to modification of its protein content, but rather it was correlated to lipid enrichment of the milk, which, in combination with profoundly altered morphology of the gland, led to impaired milk extrusion through the nipple. In summary, these data show that over-expression of autocrine hPRL in a differentiating mammary gland induces dramatic functional and morphological defects, but not carcinoma. This deserves further investigations on the emerging concept that autocrine PRL may have different effects on pathological development of the mammary gland depending on the differentiation state of the latter.