Human Prolactin Receptor: Impact of subdomain D1 of the short form variant for its inhibitory action on prolactin induced function of the long form of the receptor

Abstract

The prolactin receptor (PRLR) long form (LF) mediates diverse cellular actions of prolactin (Prl) in target tissues. Short forms (SF) through heterodimerization inhibit the LF function. Reduced SF/LF ratio in breast cancer could contribute to tumor development. Lack of dominant negative action of SF by disruption of the intra‐molecular Cys‐Cys of S1b indicated a pivotal role of the D1 domain in SF function. Mutation of E69 in the D1 (S1bX) increased homodimer formation of the expressed protein. S1bX did not inhibit Prl induced LF function on β‐casein promoter activity. Mutation of adjacent amino acids showed a similar loss of function. In contrast, SF mutants in the D2 domain at the D2/D2 interface displayed inhibitory action as the WT SF. BRET analysis showed decreased affinity in LF/S1bX heterodimers and increased S1bX/S1bX homodimers in transfected cells stably expressing LF. This in turn favors LF/LF homodimerization and Prl mediated signaling. However, the affinity of LF/SF or SF/SF was unchanged in SF with the D2 domain mutated. Molecular dynamics indicate a role of long‐range D1‐D1 electrostatic interactions and structural changes propagating down the D2 dimers. These results have demonstrated the essential role of the D1 domain on the configuration of SF for its inhibitory action on the LF mediated function. Variations in the SF D1 domain in tumor tissues could provide insights of its role in cancer development.