Regulated Binding of Importin-α to Protein Kinase Cδ in Response to Apoptotic Signals Facilitates Nuclear Import

Abstract

Background: Tyrosine phosphorylation regulates nuclear translocation of proapoptotic protein kinase C delta (PKC␦). Results: Tyrosine phosphorylation causes a conformational change that exposes the nuclear localization sequence, allowing binding of importin-␣. Conclusion: Nuclear localization of PKC␦ is regulated by access of importin-␣ to the nuclear localization sequence. Significance: Nuclear import of PKC␦, which induces apoptosis, is tightly regulated so as to prevent inappropriate cell death.

Inhibiting Tyrosine Phosphorylation of Protein Kinase Cδ (PKCδ) Protects the Salivary Gland from Radiation Damage

“…5, C and D). These studies confirm and extend previous work from our laboratory by demonstrating that c-Src and c-Abl play an essential role in DNA damageinduced apoptosis through phosphorylation of PKC␦ at Tyr-64 and Tyr-155 (11,12). To determine the potential use of TKIs to protect against salivary gland damage, we asked whether treatment with dasatinib could suppress apoptosis either in vitro or in mice exposed to head and neck IR.…”

“…We have shown previously that phosphorylation of Tyr-64 and Tyr-155 promotes a conformational change in PKC␦ leading to its association with importin-␣ and subsequent nuclear translocation (12). Our current data suggest a hierarchical relationship between Tyr-155 and Tyr-64, where phosphorylation of Tyr-155 by c-Abl serves as a permissive signal for phosphorylation of Tyr-64.…”

Protein kinase Cδ is required for ErbB2-driven mammary gland tumorigenesis and negatively correlates with prognosis in human breast cancer

“…Lysates were spun at 12,500 rpm for 20 minutes at 4°C, and supernatants from 2D and 3D culture was then separated by SDS/PAGE and immunoblotting as previously described (61). Anti-PKCδ (C-20) was purchased from Santa Cruz Biotechnology (sc-937 Santa Cruz, CA, USA).…”

“…immunoprecipitation was performed as previously described (61). Five-hundred μg of protein was incubated with primary antibody (2 μg; anti-HA; #MMS-101, Covance) or control (2 μg; anti mouse IgG; #2025; Santa Cruz Biotechnology) for three hours at 4 o C. Immunoblots were probed with the following antibodies: anti-HA (#MMS-101, Covance), Src (#8056, Santa Cruz) and PKCδ (#sc-937 Santa Cruz Biotechnology).…”

Tuning the signalling output of protein kinase C

“…Tyrosine phosphorylation can induce PKCδ’s DAG-independent activation without requiring membrane translocation and can alter its subcellular localization [26, 27]. For example, tyrosine phosphorylation of PKCδ at Tyr64 and Tyr155 in response to apoptotic stimuli induces a conformational change that exposes its nuclear localization sequence and Hsp90 binding site, allowing importin-α and Hsp90 to bind and import PKCδ into the nucleus where it can induce apoptosis [28]. H 2 O 2 -induced tyrosine phosphorylation at Tyr311 has also been proposed to activate PKCδ by inducing caspase-3 cleavage between its regulatory and catalytic domains [29].…”