Deepa Kumari, Brodsky Lab
"Regulation of a major cholesterol transporting lipoprotein at the cytosol/ER interface: Investigating roles of Hsp40s and E3 ubiquitin ligases in the biogenesis of Apolipoprotein B. "
Coronary artery disease kills 17.3 million people every year, and elevated levels of apolipoprotein B (ApoB) are a major risk factor. ApoB is the primary component of atherogenic lipoprotein particles and is responsible for the transport of dietary and endogenous fats and cholesterol. As it is synthesized, ApoB is lipidated, and forms a primordial lipoprotein particle. In contrast, in the absence of adequate lipids, ApoB is destroyed via Endoplasmic Reticulum Associated Degradation, a pathway that normally targets misfolded proteins in the early secretory pathway.
Here, we hypothesized that Hsp40s working in conjunction with Hsp70, play key roles in the biogenesis of ApoB. To this end, we investigated a panel of Hsp40s consisting of a member from each of the three Hsp40 classes in a rodent cell line that endogenously synthesizes and secretes ApoB. We observed that these Hsp40s associate with ApoB and play differential roles in ApoB biogenesis. Utilizing siRNA mediated knockdown and metabolic pulse chase experiments, we found that class A member, DNAJA1, facilitates the degradation of ApoB. However, DNAJB1, a class B member, stabilizes ApoB. Furthermore, the ablation of DNAJA1 leads to the accumulation of ubiquitinated ApoB, but DNAJB1 knockdown decreases levels of ubiquitinated ApoB suggesting differential temporal contribution. As a negative control, DNAJC19, a mitochondrial class C member, does not contribute to ApoB ERAD. We have also found that Hrd1 E3 ubiquitin ligase tags and targets ApoB for degradation. Future work will examine the lipidation state of ApoB upon Hsp40 knockdown
Friday, April 10, 2020
Virtual
12PM