Atypical Protein Kinase C ι Protects Human Leukemia Cells against Drug-induced Apoptosis

Nicole R Murray,Alan P Fields

doi:10.1074/jbc.272.44.27521

Nicole R Murray, Alan P Fields

Open Access

https://doi.org/10.1074/jbc.272.44.27521

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Abstract

Protein kinase C (PKC) isozymes play distinct roles in cellular function. In human K562 leukemia cells, PKC alpha is important for cellular differentiation and PKC betaII is required for proliferation. In this report, we assess the role of the atypical PKC isoform PKC iota in K562 leukemia cell physiology. K562 cells were stably transfected with expression plasmids containing the cDNA for human PKC iota in sense or antisense orientation to increase or decrease cellular PKC iota levels, respectively. Overexpression or inhibition of expression of PKC iota had no significant effect on the proliferative capacity of K562 cells nor their sensitivity to phorbol myristate acetate-induced cytostasis and megakaryocytic differentiation, suggesting that PKC iota does not play a critical role in these processes. Rather, PKC iota serves to protect K562 cells against drug-induced apoptosis. K562 cells, which are resistant to most apoptotic agents, undergo apoptosis when treated with the protein phosphatase inhibitor okadaic acid (OA). Overexpression of PKC iota leads to increased resistance to OA-induced apoptosis whereas inhibition of PKC iota expression sensitizes cells to OA-induced apoptosis. Overexpression of the related atypical PKC zeta has no protective effect, demonstrating that the effect is isotype-specific. PKC iota also protects K562 cells against taxol-induced apoptosis, indicating that it plays a general protective role against apoptotic stimuli. These data support a role for PKC iota in leukemia cell survival.

Highlights

Presence or absence of functional domains that confer isotypespecific co-factor and activator requirements
Protein kinase C (PKC) ␣ is involved in cellular differentiation and overexpression of PKC ␣ leads to gene dose-dependent cytostasis and increased sensitivity to differentiating agents such as phorbol myristate acetate (PMA) (8 –10)
K562 Cells Express the Atypical PKC Isoform, PKC ␫—In previous studies, we determined that the two calcium-dependent PKC isotypes expressed in human K562 leukemia cells, PKC ␣ and PKC ␤II, play distinct functional roles in K562 cell physiology [8]

Summary

Introduction

Presence or absence of functional domains that confer isotypespecific co-factor and activator requirements. We have provided direct evidence for PKC isotype specific function in the control of cellular proliferation and differentiation [8]. Immunoblot analysis with the PKC ␫-specific antibody demonstrated that these cell lines express either enhanced (Fig. 2A, lane 2) or reduced (Fig. 2A, lane 3) levels of PKC ␫, respectively, when compared with control vector-transfected cells (Fig. 2A, lane 1) or those expressing PKC ␨ (Fig. 2A, lane 4).

Results

Conclusion