Protein kinase C activator bryostatin‐1 modulates proteasome function

Abstract

Proteasome activity in ubiquitin-proteasome pathway plays a pivotal role in degradation and clearance of aggregated, oxidized, damaged, and misfolded unwanted proteins to control protein homeostasis or proteostasis. Proteasome activity decreases with cellular senescence, aging, and age-related diseases. Therefore, enhancement of impaired proteasome function by molecular biological and/or pharmacological intervention is an active area of research. Bryostatin-1, a naturally occurring macrocyclic lactone, activates PKC isozymes (specifically, -α and -ϵ) at sub-nanomolar concentrations, but downregulates at higher concentrations. Here, we present bryostatin-1 increased chymotrypsin-like proteasome activity of 20S assembly at sub-nanomolar to nanomolar concentrations (0.3-30 nM). However, proteasome activity decreased at a micromolar concentration of bryostatin-1 (AG08044 cultured skin: P < 0.005; differentiated SH-SY5Y cells: P < 0.02). Modulation of proteasome function by bryostatin-1 was studied in six dermal fibroblast primary cell lines developed both from freshly taken biopsies from healthy donors (n = 2) and obtained from well-characterized cell repositories (n = 4; without any diseases). Bryostatin-1 enhanced proteasome activity in cultured skin fibroblasts obtained from banked and freshly isolated skin fibroblasts from skin biopsies at the sub-nanomolar concentration (P < 0.015). Modulation of proteasome function by bryostatin-1 was confirmed in neuron-like differentiated SH-SY5Y cells. Direct additions of bryostatin-1 into cell lysates prepared from neuron-like differentiated SH-SY5Y, Jurkat cells, and cultured skin fibroblasts were unable to increase proteasome activity indicating that bryostatin-1 can only modulate proteasome activity when added to live cell culture systems. Standard PKC inhibitors blocked bryostatin-1 induced proteasome activity modulation suggesting that enhancement of proteasome activity was mediated by PKC modulation.