Obesity results when caloric intake exceeds metabolic needs over an extended period of time. The condition predicates heart disease and diabetes – two pathologies that diminish the quality of life and increase risk of premature death. Melanin-concentrating hormone (MCH) acts via a G protein-coupled receptor on the plasma membrane of neurons to stimulate appetite, and fat cells to stimulate feedback secretion of leptin. Dysregulation of MCH signaling is hypothesized to be a contributing factor in select appetite disorders. Little is known about how cells regulate MCH receptor signaling however plasma membrane localization of MCHR1 has been implicated as a contributing factor. We previously reported that caveolae, a cholesterol like protein, enhances MCH signaling in CHO cells. This, together with recent reports of MCHR1 localization to primary cilia in neurons located in the hypothalamus led us to hypothesize that organization of MCHR1 in the plasma membrane might be important to MCH function in other cell types as well. When VSVg-tagged MCHR1 is expressed in CHO-K1 cells, the tagged receptor can be found on the plasma membrane, but occasionally localizes to two small dots near the nucleus, particularly after starvation. We next studied two cell lines which naturally express the receptor: human SH-SY5Y neuroblastoma cells and murine 3T3-L1 pre-adipocytes, which both responded to MCH by activating ERK. Using immunostaining, diffuse plasma membrane-localized MCHR2 was detected in SH-SY5Y cells. Although MCHR1 plasma membrane expression was confirmed in both SH-SY5Ys and 3T3-L1s, both cell types had distinctive MCHR1 patterning; SH-SY5Ys had clusters of MCHR1-positive vesicles and 3T3-L1 cells revealed MCHR1-positive primary cilia during differentiation. Together, these results suggest movement of MCHR1 to a centrosomal-location prepares receptor for entry into primary cilia, and that a role for primary cilia in the regulation of receptor signaling may be more widespread than originally thought. Future experiments will be aimed at determining the role that this localization plays in the regulation of MCH signaling.
|Presenter:||Bryan H. Pratt (Graduate Student)|
|Time:||10:45 am (Session II)
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