HSPB1 facilitates ERK-mediated phosphorylation and degradation of BIM to attenuate endoplasmic reticulum stress-induced apoptosis

BIM, a pro-apoptotic BH3-only protein, is a key regulator of the intrinsic (or mitochondrial) apoptosis pathway. Here, we show that BIM induction by endoplasmic reticulum (ER) stress is suppressed in rat PC12 cells overexpressing heat shock protein B1 (HSPB1 or HSP27) and that this is due to enhanced proteasomal degradation of BIM. HSPB1 and BIM form a complex that immunoprecipitates with p-ERK1/2. We found that HSPB1-mediated proteasomal degradation of BIM is dependent on MEK-ERK signaling. Other studies have shown that several missense mutations in HSPB1 cause the peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease, which is associated with nerve degeneration. Here we show that cells overexpressing CMT-related HSPB1 mutants exhibited increased susceptibility to ER stress-induced cell death and high levels of BIM. These findings identify a novel function for HSPB1 as a negative regulator of BIM protein stability leading to protection against ER stress-induced apoptosis, a function that is absent in CMT-associated HSPB1 mutants

MIROs and DRP1 drive mitochondrial-derived vesicle biogenesis and promote quality control

By characterizing the composition of mitochondrial-derived vesicles (MDVs), Konig et al. define a MIRO1/2- and DRP1-dependent MDV biogenesis pathway and propose that MDVs maintain the mitochondrial proteome by shuttling assembled protein complexes to lysosomes. Mitochondrial-derived vesicles (MDVs) are implicated in diverse physiological processes-for example, mitochondrial quality control-and are linked to various neurodegenerative diseases. However, their specific cargo composition and complex molecular biogenesis are still unknown. Here we report the proteome and lipidome of steady-state TOMM20(+) MDVs. We identified 107 high-confidence MDV cargoes, which include all beta-barrel proteins and the TOM import complex. MDV cargoes are delivered as fully assembled complexes to lysosomes, thus representing a selective mitochondrial quality control mechanism for multi-subunit complexes, including the TOM machinery. Moreover, we define key biogenesis steps of phosphatidic acid-enriched MDVs starting with the MIRO1/2-dependent formation of thin membrane protrusions pulled along microtubule filaments, followed by MID49/MID51/MFF-dependent recruitment of the dynamin family GTPase DRP1 and finally DRP1-dependent scission. In summary, we define the function of MDVs in mitochondrial quality control and present a mechanistic model for global GTPase-driven MDV biogenesis

Hspb1 facilitates erk-mediated phosphorylation and degradation of bim to attenuate endoplasmic reticulum stress-induced apoptosis

BIM, a pro-apoptotic BH3-only protein, is a key regulator of the intrinsic (or mitochondrial) apoptosis pathway. Here, we show that BIM induction by endoplasmic reticulum (ER) stress is suppressed in rat PC12 cells overexpressing heat shock protein B1 (HSPB1 or HSP27) and that this is due to enhanced proteasomal degradation of BIM. HSPB1 and BIM form a complex that immunoprecipitates with p-ERK1/2. We found that HSPB1-mediated proteasomal degradation of BIM is dependent on MEK-ERK signaling. Other studies have shown that several missense mutations in HSPB1 cause the peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease, which is associated with nerve degeneration. Here we show that cells overexpressing CMT-related HSPB1 mutants exhibited increased susceptibility to ER stress-induced cell death and high levels of BIM. These findings identify a novel function for HSPB1 as a negative regulator of BIM protein stability leading to protection against ER stress-induced apoptosis, a function that is absent in CMT-associated HSPB1 mutants

Hspb1 facilitates erk-mediated phosphorylation and degradation of bim to attenuate endoplasmic reticulum stress-induced apoptosis

BIM, a pro-apoptotic BH3-only protein, is a key regulator of the intrinsic (or mitochondrial) apoptosis pathway. Here, we show that BIM induction by endoplasmic reticulum (ER) stress is suppressed in rat PC12 cells overexpressing heat shock protein B1 (HSPB1 or HSP27) and that this is due to enhanced proteasomal degradation of BIM. HSPB1 and BIM form a complex that immunoprecipitates with p-ERK1/2. We found that HSPB1-mediated proteasomal degradation of BIM is dependent on MEK-ERK signaling. Other studies have shown that several missense mutations in HSPB1 cause the peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease, which is associated with nerve degeneration. Here we show that cells overexpressing CMT-related HSPB1 mutants exhibited increased susceptibility to ER stress-induced cell death and high levels of BIM. These findings identify a novel function for HSPB1 as a negative regulator of BIM protein stability leading to protection against ER stress-induced apoptosis, a function that is absent in CMT-associated HSPB1 mutants

ORMDL3 expression levels have no influence on the activity of serine palmitoyltransferase.

ORMDL proteins are believed to be negative regulators of serine palmitoyltransferase (SPT), which catalyzes the first and rate limiting step in sphingolipid (SL) de novo synthesis. Several single-nucleotide polymorphisms (SNPs) that are close to the ORMDL3 locus have been reported to increase ORMDL3 expression and to be associated with an elevated risk for early childhood asthma; however, the direct effect of ORMDL3 expression on SPT activity and its link to asthma remains elusive. In this study, we investigated whether ORMDL3 expression is associated with changes in SPT activity and total SL levels. Ormdl3-knockout (Ormdl3(-/-)) and transgenic (Ormdl3(Tg/wt)) mice were generated to study the effect of ORMDL3 on total SL levels in plasma and tissues. Cellular SPT activity was measured in mouse embryonic fibroblasts from Ormdl3(-/-) mice, as well as in HEK293 cells in which ORMDL3 was overexpressed and silenced. Furthermore, we analyzed the association of the reported ORMDL3 asthma SNPs with plasma sphingoid bases in a population-based cohort of 971 individuals. Total C18-long chain bases were not significantly altered in the plasma and tissues of Ormdl3(-/-) mice, whereas C18-sphinganine showed a small and significant increase in plasma, lung, and liver tissues. Mouse embryonic fibroblast cells from Ormdl3(-/-) mice did not show an altered SPT activity compared with Ormdl3(+/-) and Ormdl3(+/+) mice. Overexpression or knockdown of ORMDL3 in HEK293 cells did not alter SPT activity; however, parallel knockdown of all 3 ORMDL isoforms increased enzyme activity significantly. A significant association of the annotated ORMDL3 asthma SNPs with plasma long-chain sphingoid base levels could not be confirmed. ORMDL3 expression levels seem not to be directly associated with changes in SPT activity. ORMDL3 might influence de novo sphingolipid metabolism downstream of SPT.-Zhakupova, A., Debeuf, N., Krols, M., Toussaint, W., Vanhoutte, L., Alecu, I., Kutalik, Z., Vollenweider, P., Ernst, D., von Eckardstein, A., Lambrecht, B. N., Janssens, S., Hornemann, T. ORMDL3 expression levels have no influence on the activity of serine palmitoyltransferase