RESUMO
Coatomer complexes function in the sorting and trafficking of proteins between subcellular organelles. Pathogenic variants in coatomer subunits or associated factors have been reported in multi-systemic disorders, i.e., coatopathies, that can affect the skeletal and central nervous systems. We have identified loss-of-function variants in COPB2, a component of the coatomer complex I (COPI), in individuals presenting with osteoporosis, fractures, and developmental delay of variable severity. Electron microscopy of COPB2-deficient subjects' fibroblasts showed dilated endoplasmic reticulum (ER) with granular material, prominent rough ER, and vacuoles, consistent with an intracellular trafficking defect. We studied the effect of COPB2 deficiency on collagen trafficking because of the critical role of collagen secretion in bone biology. COPB2 siRNA-treated fibroblasts showed delayed collagen secretion with retention of type I collagen in the ER and Golgi and altered distribution of Golgi markers. copb2-null zebrafish embryos showed retention of type II collagen, disorganization of the ER and Golgi, and early larval lethality. Copb2+/- mice exhibited low bone mass, and consistent with the findings in human cells and zebrafish, studies in Copb2+/- mouse fibroblasts suggest ER stress and a Golgi defect. Interestingly, ascorbic acid treatment partially rescued the zebrafish developmental phenotype and the cellular phenotype in Copb2+/- mouse fibroblasts. This work identifies a form of coatopathy due to COPB2 haploinsufficiency, explores a potential therapeutic approach for this disorder, and highlights the role of the COPI complex as a regulator of skeletal homeostasis.
Assuntos
Osso e Ossos/metabolismo , Complexo I de Proteína do Envoltório/genética , Proteína Coatomer/genética , Deficiências do Desenvolvimento/genética , Deficiência Intelectual/genética , Osteoporose/genética , Animais , Ácido Ascórbico/farmacologia , Osso e Ossos/efeitos dos fármacos , Osso e Ossos/patologia , Encéfalo/diagnóstico por imagem , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Encéfalo/patologia , Criança , Pré-Escolar , Complexo I de Proteína do Envoltório/deficiência , Proteína Coatomer/química , Proteína Coatomer/deficiência , Colágeno Tipo I/genética , Colágeno Tipo I/metabolismo , Deficiências do Desenvolvimento/diagnóstico por imagem , Deficiências do Desenvolvimento/metabolismo , Deficiências do Desenvolvimento/patologia , Embrião não Mamífero , Retículo Endoplasmático/efeitos dos fármacos , Retículo Endoplasmático/metabolismo , Retículo Endoplasmático/patologia , Feminino , Fibroblastos/efeitos dos fármacos , Fibroblastos/metabolismo , Fibroblastos/patologia , Regulação da Expressão Gênica no Desenvolvimento , Complexo de Golgi , Haploinsuficiência , Humanos , Deficiência Intelectual/diagnóstico por imagem , Deficiência Intelectual/metabolismo , Deficiência Intelectual/patologia , Masculino , Camundongos , Osteoporose/tratamento farmacológico , Osteoporose/metabolismo , Osteoporose/patologia , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/metabolismo , Índice de Gravidade de Doença , Peixe-ZebraRESUMO
Cancer stem cells (CSCs) may be responsible for tumour dormancy, relapse and the eventual death of most cancer patients. In addition, these cells are usually resistant to cytotoxic conditions. However, very little is known about the biology behind this resistance to therapeutics. Here we investigated stem-cell death in the digestive system of adult Drosophila melanogaster. We found that knockdown of the coat protein complex I (COPI)-Arf79F (also known as Arf1) complex selectively killed normal and transformed stem cells through necrosis, by attenuating the lipolysis pathway, but spared differentiated cells. The dying stem cells were engulfed by neighbouring differentiated cells through a draper-myoblast city-Rac1-basket (also known as JNK)-dependent autophagy pathway. Furthermore, Arf1 inhibitors reduced CSCs in human cancer cell lines. Thus, normal or cancer stem cells may rely primarily on lipid reserves for energy, in such a way that blocking lipolysis starves them to death. This finding may lead to new therapies that could help to eliminate CSCs in human cancers.
Assuntos
Transformação Celular Neoplásica/metabolismo , Transformação Celular Neoplásica/patologia , Drosophila melanogaster/citologia , Drosophila melanogaster/metabolismo , Lipólise/fisiologia , Células-Tronco Neoplásicas/metabolismo , Células-Tronco Neoplásicas/patologia , Fator 1 de Ribosilação do ADP/antagonistas & inibidores , Fator 1 de Ribosilação do ADP/deficiência , Animais , Apoptose , Autofagia , Diferenciação Celular , Linhagem Celular Tumoral , Proliferação de Células , Sobrevivência Celular/efeitos dos fármacos , Transformação Celular Neoplásica/efeitos dos fármacos , Complexo I de Proteína do Envoltório/deficiência , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Resistencia a Medicamentos Antineoplásicos/efeitos dos fármacos , Metabolismo Energético , Enterócitos/citologia , Feminino , Trato Gastrointestinal/patologia , Humanos , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Lipólise/efeitos dos fármacos , Sistema de Sinalização das MAP Quinases , Masculino , Proteínas de Membrana/metabolismo , Necrose/induzido quimicamente , Células-Tronco Neoplásicas/efeitos dos fármacos , Fagocitose , Proteínas rac de Ligação ao GTP/metabolismoRESUMO
Retrograde transport dependent on coat protein I (COPI) was impaired using two different approaches and the effects on the retrograde transport of protein toxins were investigated. One approach was to study ldlF cells that express a temperature-sensitive defect in the epsilon-COP subunit of COPI. The second approach was to treat cells with 1,3-cyclohexanebis(methylamine) (CBM), a drug that interferes with the binding of COPI to Golgi membranes. With both approaches, cells remained sensitive to a variety of protein toxins regardless of whether the toxins contained a KDEL motif. Moreover, cholera toxin, which contains a KDEL sequence, was observed by immunofluorescence microscopy to enter the endoplasmic reticulum of Vero cells in the presence of CBM. These data support published evidence indicating the presence in cells of a COPI- and KDEL receptor-independent pathway of retrograde transport from the Golgi complex to the endoplasmic reticulum. In addition, the results suggest that certain toxins containing a KDEL motif may use either the COPI-dependent or COPI-independent pathway of retrograde transport.
