Bcl10 crucially nucleates the pro-apoptotic complexes comprising PDK1, PKCζ and caspase-3 at the nuclear envelope of etoposide-treated human cervical carcinoma C4-I cells

Protein kinase  (PK)Cζ signaling at various subcellularlevels affects cell survival, differentiation, growth and/or apoptosis. However, the mechanisms modulating PKCζ activity at the nuclear membrane  (NM) are not yet fully understood. Previously, we demonstrated that PKCζ interacts with the B‑-cell lymphoma  10  (Bcl10) protein at the NM of human cervical carcinoma  (HCC) C4‑-I cells. In the present study, we aimed to further clarify the interactions between PKCζ, Bcl10 and other proteins co-immunoprecipitated from NMs isolated from untreated and etoposide (also known as VP‑-16; 2.0  µg/ml)‑-treated C4‑-I cells using biochemical and proteomics analyses. Aside from the Bcl10 protein, 3‑-phosphoinositide‑-dependent protein kinase‑-1  (PDK1) also co-immunoprecipitated with PKCζ from NMs of C4‑-I cells, indicating the assembly of a heterotrimeric complex, which increased with time in VP‑-16‑-exposed cells, as did the activity of PDK1‑-phosphorylated‑-PKCζ. In turn, PKCζ‑-phosphorylated‑-Bcl10 straddled an enlarged complex which comprised caspase‑-3. Subsequently, activity‑-enhanced caspase‑-3 cleaved and inactivated PKCζ. Finally, the suppressionof Bcl10 using specific siRNA or lentiviral transduction prevented the increase in the PDK1•PKCζ association, the increase in the activity of PKCζ and caspase‑-3, as well as the caspase‑-3‑-mediated PKCζ proteolysis and inactivation from occurring at the NMs of the VP‑-16‑-exposed C4‑-I cells. Our observations provide evidence that Bcl10 acts as a pivotal pro-apoptotic protein which crucially nucleates complexes comprising PDK1, PKCζ and active caspase‑-3 at the NMs of VP‑-16‑-exposed C4‑-I cells. Hence, our data suggest that Bcl10 and PKCζ are potential therapeutic targets in the treatment of HCC