EXPRESSION OF A PROLACTIN-LIKE FACTOR IN PRENEOPLASTIC AND NEOPLASTICMOUSE MAMMARY-GLAND AND CELLS

Prolactin is a member of the growth hormone family and is required for the growth and terminal differentiation of the mammary gland. Ectopic production of this hormone has been reported in including rat, sheep, goat and mammary tissues. In this study, mouse mammary cell lines, xe nographs in the mammary gland from these cell lines and from hyperplas tic alveolar nodules, spontaneous tumors, and normal tissues were stud ied for de novo production of this growth factor. Prolactin transcript s were found by reverse transcriptase PCR in some neoplastic and prene oplastic tissues and in mouse mammary cell lines, NOG8 and CDNR4, but were not detected in the normal mouse mammary gland. Northern analysis revealed a 1 kb transcript for both cell lines that co-migrated with the prolactin pituitary transcript. Conditioned medium from NOG8 cells was positive for prolactin bioactivity by the Nb2 rat lymphoma cell p roliferation assay, and Western analysis revealed the presence of immu noreactive proteins at M(r) 14 000 and 60 000. Prolactin-like bioactiv ity was not detected in conditioned medium from CDNR4 cells, but an im munoreactive protein of M(r) 60 000 was detected by Western analysis. The mouse mammary cell line, Comma D, was negative for prolactin trans cripts; however, adenocarcinomas derived from inoculation of Comma D c ells into the cleared mammary fat pad were positive by reverse transcr iptase PCR in two of four cases. Hyperplastic outgrowths maintained in the cleared mammary fat pad as well as spontaneous tumors were positi ve for prolactin transcripts in one of four cases. These results sugge st that prolactin can be produced ectopically by the neoplastic mouse mammary gland.