Ligand-independent homo- and heterodimerization of human prolactin receptor variants: inhibitory action of the short forms by heterodimerization

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Published on Friday, 22 January 2021

Abstract

Prolactin (PRL) acts through the long form (LF) of the human PRL receptor (hPRLR) to cause differentiation of mammary epithelial cells through activation of the Janus kinase-2 (JAK2)/signal transducer and activator of transcription 5 (STAT5) pathway and subsequent transcriptional events.

To determine whether the inhibitory action of hPRLR short forms (SFs; S1a and S1b) on PRL-induced signal transduction through the LF results from heterodimerization, we studied complex formation among variant forms of the hPRLR. 3'-Tagged fusion constructs, with activities comparable to the wild-type species, were used to investigate homodimer and heterodimer formation. The LF and both SFs of the hPRLR formed homodimers under nonreducing conditions, independently of PRL, but formed only monomers under reducing conditions.

Coimmunoprecipitation of the cotransfected LF with the SFs (S1a or S1b) in transfected cells showed ligand-independent heterodimerization of individual SFs with the LF.

Bioluminescence resonance energy transfer analysis demonstrated homo- and heterodimeric associations of hPRLR variants in human embryonic kidney 293 cells.

Biotin-avidin immunoprecipitation analysis revealed that hPRLR forms are cell surface receptors and that SFs do not influence the steady state or half-life of the LF. Significant homo- and heterodimerization of biotinylated membrane hPRLR forms was observed.

These findings indicate that homo- and heterodimers of hPRLR are constitutively present, and that the bivalent hormone acts on the preformed LF homodimer to induce the active signal transduction configuration.

Although SF homodimers and their heterodimers with LF mediate JAK2 activation, the SF heterodimer partner lacks cytoplasmic sequences essential for activation of the JAK2/signal transducer and activator of transcription 5 pathway. This prevents the heterodimeric LF from mediating activation of PRL-induced genes.

 

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- Publication, 2019 Sep: Effects of Somatostatin and Vitamin C on the Fatty Acid Profile of Breast Cancer Cell Membranes (from Di Bella's Foundation);

- Publication, 2019 Sep: Effects of somatostatin, curcumin, and quercetin on the fatty acid profile of breast cancer cell membranes (from Di Bella's Foundation);

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- The Synergism of Somatostatin, Melatonin, Vitamins Prolactin and Estrogen Inhibitors Increased Survival, Objective Response and Performance Status In 297 Cases of Breast Cancer;

- Complete objective response, stable for 5 years, with the Di Bella Method, of multiple-metastatic carcinoma of the breast;

- Evaluation of the safety and efficacy of the first-line treatment with somatostatin combined with melatonin, retinoids, vitamin D3, and low doses of cyclophosphamide in 20 cases of breast cancer: a preliminary report;

- The Di Bella Method (DBM) improved survival, objective response and performance status in a retrospective observational clinical study on 122 cases of breast cancer;

- Complete objective response to biological therapy of plurifocal breast carcinoma.