RESUMO
The dipeptide glycyl-l-phenylalanine 2-naphthylamide (GPN) is widely used to perturb lysosomes because its cleavage by the lysosomal enzyme cathepsin C is proposed to rupture lysosomal membranes. We show that GPN evokes a sustained increase in lysosomal pH (pHly), and transient increases in cytosolic pH (pHcyt) and Ca2+ concentration ([Ca2+]c). None of these effects require cathepsin C, nor are they accompanied by rupture of lysosomes, but they are mimicked by structurally unrelated weak bases. GPN-evoked increases in [Ca2+]c require Ca2+ within the endoplasmic reticulum (ER), but they are not mediated by ER Ca2+ channels amplifying Ca2+ release from lysosomes. GPN increases [Ca2+]c by increasing pHcyt, which then directly stimulates Ca2+ release from the ER. We conclude that physiologically relevant increases in pHcyt stimulate Ca2+ release from the ER in a manner that is independent of IP3 and ryanodine receptors, and that GPN does not selectively target lysosomes.
Assuntos
Sinalização do Cálcio/efeitos dos fármacos , Cálcio/metabolismo , Citosol/efeitos dos fármacos , Dipeptídeos/farmacologia , Retículo Endoplasmático/efeitos dos fármacos , Transporte Biológico , Sistemas CRISPR-Cas , Canais de Cálcio/genética , Canais de Cálcio/metabolismo , Catepsina C/genética , Catepsina C/metabolismo , Linhagem Celular Tumoral , Citosol/metabolismo , Retículo Endoplasmático/metabolismo , Edição de Genes , Expressão Gênica , Técnicas de Silenciamento de Genes , Células HEK293 , Células HeLa , Humanos , Concentração de Íons de Hidrogênio/efeitos dos fármacos , Receptores de Inositol 1,4,5-Trifosfato/genética , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Leucócitos/citologia , Leucócitos/efeitos dos fármacos , Leucócitos/metabolismo , Proteínas de Membrana Lisossomal/genética , Proteínas de Membrana Lisossomal/metabolismo , Lisossomos/efeitos dos fármacos , Lisossomos/metabolismo , Ploidias , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismoRESUMO
Synthetic full agonists of PPARγ have been prescribed for the treatment of diabetes due to their ability to regulate glucose homeostasis and insulin sensitization. While the use of full agonists of PPARγ has been hampered due to severe side effects, partial agonists have shown promise due to their decreased incidence of such side effects in preclinical models. No kinetic information has been forthcoming in regard to the mechanism of full versus partial agonism of PPARγ to date. Here, we describe the discovery of a partial agonist, SR2067. A co-crystal structure obtained at 2.2 Å resolution demonstrates that interactions with the ß-sheet are driven exclusively via hydrophobic interactions mediated through a naphthalene group, an observation that is unique from other partial agonists. Surface plasmon resonance revealed that SR2067 binds to the receptor with higher affinity (KD = 513 nM) as compared to that of full agonist rosiglitazone, yet it has a much slower off rate compared to that of rosiglitazone.
