Multiple internalization motifs differentially used by prolactin receptor isoforms mediate similar endocytic pathways

Area of Science:

• Endocrinology
• Cell Biology
• Molecular Biology

Background:

• Prolactin (PRL) is a hormone regulating diverse physiological functions.
• Two isoforms of the prolactin receptor (PRLR), long (lPRLR) and short (sPRLR), exist with distinct signaling capacities.
• Understanding PRLR isoform trafficking is crucial for comprehending PRL's cellular effects.

Purpose of the Study:

• To compare the endocytosis mechanisms of bovine lPRLR and sPRLR isoforms.
• To identify specific motifs involved in lPRLR internalization.
• To elucidate how differences in endocytosis affect PRLR signaling.

Main Methods:

• Comparative analysis of lPRLR and sPRLR endocytosis in bovine cells.
• Site-directed mutagenesis to identify key internalization motifs (phenylalanine, dileucine).
• Expression of truncated and mutant PRLR constructs, including cT272.
• Manipulation of endocytic pathway components (dynamin, clathrin hub).

Main Results:

• The lPRLR exhibits significantly faster internalization than the sPRLR.
• Multiple motifs, including phenylalanine (F290) and dileucines near amino acid 272, are essential for lPRLR internalization.
• A truncated lPRLR (cT272) internalizes at the same rate as the full-length lPRLR.
• The dileucine motifs shared by sPRLR mediate similar endocytic pathways to lPRLR, despite slower rates.

Conclusions:

• Cellular trafficking of PRLR isoforms is differentially regulated by specific amino acid motifs.
• Faster lPRLR endocytosis contributes to short-term signaling downregulation.
• These findings enhance understanding of prolactin's control over target cell responsiveness.