Elevated calpain activity in acute myelogenous leukemia correlates with decreased calpastatin expression

Abstract

Calpains are intracellular cysteine proteases that have crucial roles in many physiological and pathological processes. Elevated calpain activity has been associated with many pathological states. Calpain inhibition can be protective or lethal depending on the context. Previous work has shown that c-myc transformation regulates calpain activity by suppressing calpastatin, the endogenous negative regulator of calpain. Here, we have investigated calpain activity in primary acute myelogenous leukemia (AML) blast cells. Calpain activity was heterogeneous and greatly elevated over a wide range in AML blast cells, with no correlation to FAB classification. Activity was particularly elevated in the CD34+CD38− enriched fraction compared with the CD34+CD38+ fraction. Treatment of the cells with the specific calpain inhibitor, PD150606, induced significant apoptosis in AML blast cells but not in normal equivalent cells. Sensitivity to calpain inhibition correlated with calpain activity and preferentially targeted CD34+CD38− cells. There was no correlation between calpain activity and p-ERK levels, suggesting the ras pathway may not be a major contributor to calpain activity in AML. A significant negative correlation existed between calpain activity and calpastatin, suggesting calpastatin is the major regulator of activity in these cells. Analysis of previously published microarray data from a variety of AML patients demonstrated a significant negative correlation between calpastatin and c-myc expression. Patients who achieved a complete remission had significantly lower calpain activity than those who had no response to treatment. Taken together, these results demonstrate elevated calpain activity in AML, anti-leukemic activity of calpain inhibition and prognostic potential of calpain activity measurement.

Glucopsychosine increases cytosolic calcium to induce calpain-mediated apoptosis of acute myeloid leukemia cells

“…A second feature of AML cells that would render them sensitive to glucopsychosine is the recent observation that calpain levels are significantly elevated while calpastatin, a calpain inhibitor, is significantly reduced in AML cells compared to normal hematopoietic cells [44].…”

“…This mode of death may be particularly important to a subset of AML patients, as it was recently shown that calpain levels in AML cells may be an important prognostic indicator. Niapour et al (2012) showed that patients samples with elevated cellular calpain levels had no response to PD150606 (a calpain inhibitor) whereas patient samples with low calpain levels were associated with improved complete response rates [44]. Thus, application of a stimulus to increase calpain in AML cells with already elevated calpain would be a novel approach at inducing a response in these patients, which do not respond to conventional therapy.…”

“…This has implications in regards to cancer cell morphology because calpains therefore promote oncogenesis within cells. Niapour et al [44] has…”

“…6B, right panel). Finally, it has been shown that AML cells have upregulated levels of calpain [44]. To determine if calpain levels were a predictor of glucopsychosine's ability to induce death, we tested calpain protein levels in multiple glucopsychosine sensitive cell lines and compared them to cells lines that were less sensitive to glucopsychosine treatment by Western blot analysis (Fig.…”

“…Calpain activity has been reported in numerous pathological states to be increased. Niapour et al (2012) [44] showed that calpain activity is highly elevated in the CD34+/CD38-populations of AML subtypes. The elevated levels of calpains conferred a pro-survival mechanism because treatment with PD150606 (a calpain inhibitor) induced apoptosis [44].…”