Characterization of a prolactin-inducible gene, clone 15, in T cells.

To examine how PRL regulates lymphocyte proliferation, a number of PRL-activated genes were identified from a PRL-dependent rat T lymphoma cell line, Nb2. One of the downstream genes in the PRL signaling cascade was identified as clone 15 (c15). PRL stimulation of quiescent Nb2 T cells results in the expression of a 1.7-kilobase c15 mRNA, which reaches maximum levels between 8 and 10 h after stimulation. Corresponding [3H]thymidine incorporation experiments show that the maximum level of c15 mRNA expression correlates with the G1/S transition phase of the cell cycle. Sequencing of approximately 1.3-kilobase cDNA revealed one open reading frame that predicts a 332-amino acid protein. In vitro transcription/translation of c15 cDNA resulted in the production of a 45-kilodalton protein. Sequence analysis revealed that the c15 open reading frame contains a potential nuclear localization signal, a very acidic region, and a carboxy-terminal region of 94 amino acids which are 68% identical and 78% similar to the nuclear movement protein, NUDC, found in Aspergillus nidulans. Such a high degree of conservation suggests that the NUDC-like motif in c15 has been conserved through evolution for an important structure and/or function.