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The activation of inactive membrane-associated protein kinase C is associated with DMSO-induced erythroleukemia cell
B R Chakravarthy1, R Tremblay, P Macdonald
1Institute for Biological Sciences, National Research Council of Canada, Ottawa.
Abstract:
The rapid redistribution of cytosolic protein kinase C (PKC) to membranes and its subsequent proteolytic activation to PKM have been implicated in the DMSO/HMBA-induced differentiation of murine erythroleukemia (MEL) cells. However, DMSO was found not to induce detectable changes in PKC distribution in a MEL cell subline (MEL1) which differentiated normally in response to the agent. Nevertheless, the differentiation of MEL1 cells appeared dependent on an early PKC-related event because hemoglobinization was partially blocked by the PKC inhibitor H-7 added to cells within the first 2 h after DMSO induction. Indeed, a rapid (15-60 min) increase in membrane PKC activity was detected in DMSO-treated MEL1 cells using a novel method which quantitates the amount of 'active' PKC in intact membranes. This transient PKC increase resulted from the activation of 'inactive' enzyme already associated with membranes, and not from the translocation of cytosolic PKC. Conventional PKC assays cannot distinguish between active and inactive membrane PKC pools. DMSO also activated inactive membrane PKC in HL-60 cells, but not in S49T-lymphoma and WEHI-231 B-lymphoma cells which do not differentiate in response to DMSO. The results suggest that a rapid and transient increase in membrane PKC activity may be an important early step in DMSO-induced differentiation of erythroleukemia cells.
Insights
Dimethyl sulfoxide (DMSO) induces differentiation in murine erythroleukemia (MEL) cells by activating membrane-bound protein kinase C (PKC). This early event, not involving cytosolic redistribution, is crucial for DMSO-induced MEL cell differentiation.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Protein Kinase C (PKC) redistribution and activation are linked to DMSO/HMBA-induced murine erythroleukemia (MEL) cell differentiation.
- A MEL cell subline (MEL1) differentiates normally with DMSO but shows no detectable cytosolic PKC redistribution.
Purpose of the Study:
- To investigate the role of PKC activation in MEL1 cell differentiation.
- To determine if DMSO induces changes in membrane-associated PKC activity in MEL1 cells.
Main Methods:
- Utilized a novel method to quantify 'active' PKC in intact membranes of DMSO-treated MEL1 cells.
- Compared PKC activity changes in MEL1 cells with HL-60, S49T-lymphoma, and WEHI-231 B-lymphoma cells.
Main Results:
- DMSO treatment of MEL1 cells caused a rapid, transient increase in membrane PKC activity within 15-60 minutes.
- This increase resulted from the activation of existing inactive membrane PKC, not cytosolic translocation.
- DMSO also activated inactive membrane PKC in HL-60 cells, but not in non-differentiating lymphoma cell lines.
Conclusions:
- A rapid, transient increase in membrane-associated PKC activity is a key early step in DMSO-induced erythroleukemia cell differentiation.
- This activation mechanism differs from the previously assumed cytosolic PKC redistribution model.
- The findings highlight a novel role for membrane-bound PKC in cellular differentiation processes.