Elephant shark melanocortin receptors: Novel interactions with MRAP1 and implication for the HPI axis

• Published in: General and comparative endocrinology Vol. 272; no. C; pp. 42 - 51
• Main Authors: Barney, Emily, Dores, Michael R., McAvoy, Danielle, Davis, Perry, Racareanu, Rona-Cristina, Iki, Ayuko, Hyodo, Susumu, Dores, Robert M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2019; Elsevier
• Subjects: Adrenocorticotropic Hormone - metabolism; Animals; Elephant shark; Fishes; HPI; Melanocortin receptors; MRAP1; MRAP2; Receptor, Melanocortin, Type 1 - metabolism; Receptor, Melanocortin, Type 2 - metabolism; Receptors, Melanocortin - genetics; Sharks; HPI; MRAP2; Elephant shark; MRAP1; Melanocortin receptors
• ISSN: 0016-6480; 1095-6840
• DOI: 10.1016/j.ygcen.2018.11.009

•RT-PCR analysis detected gMrap1, gMc2r, gMc5r, and gMc3r mRNA in interrenal tissue.•Co-expression of gMc2R/gMrap1in CHO cells increased sensitivity to stimulation by ACTH(1–24) 10 fold.•Co-expression of gMc5R/gMrap1 in CHO cells increased sensitivity to stimulation by ACTH(1–24) 100 fold.•Co-expression with gMrap1 did not increase trafficking of either gMc2r or gMc5r to the PM.•Imaging analyses indicated that gMC2R/gMrap1, and gMc5r/gMrap1 are co-localized on the PM. The presence of Mrap1 and Mrap2 orthologs in the genome of the elephant shark (es), a cartilaginous fish, presented an opportunity to evaluate the potential interactions between these accessory proteins and melanocortin receptors of a cartilaginous fish. RT-PCR analysis indicated that Mrap1 mRNA was present in interrenal, brain, and pituitary tissue with mRNA for Mc2R, Mc3R, Mc4R, and Mc5r. Co-expression of esMrap1 cDNA with esMc2r cDNA or esMc5r cDNA in CHO cells increased sensitivity to stimulation with ACTH(1–24) 10 fold and 100 fold, respectfully, but had no effect on sensitivity to stimulation with DesAc-αMSH [i.e., ACTH(1–13)NH2] for either receptor, and had no effect on the ligand sensitivity of either esMc3r or esMc4r. Fluorescence image analysis indicated co-localization of esMrap1/esMc2r, and esMrap1/esMc5r on the plasma membrane; however, cell surface ELISA analysis indicated that co-expression with esMrap1 had no effect, positive or negative, on the trafficking of either esMc2r or esMc5r to the plasma membrane. RT-PCR analysis also indicated that Mrap2 mRNA, as well as, mRNAs for Mc2r, Mc3r, Mc4r, and Mc5r could be detected in brain tissue, however no Mrap2 mRNA was detected in interrenal tissue. Co-expression of esMrap2 in CHO cells with, respectively, esMc2r, esMc4r, or esMc5r had no effect on ligand sensitivity. However, co-expression of esMrap2 with esMc3r did lower sensitivity to stimulation by DesAc-αMSH 10 fold. These observations are discussed in the context of the parallel evolution of melanocortin receptors and their accessory proteins, and the hypothalamus/pituitary/adrenal axis and the hypothalamus/pituitary/interrenal axis in bony vertebrates and cartilaginous fishes.