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Novel protein inhibitor of calmodulin-dependent cyclic nucleotide phosphodiesterase from glioblastoma multiforme
1Department of Surgery, College of Medicine, Royal University Hospital, University of Saskatchewan, Saskatoon, Canada.
Abstract:
Previous investigations from our laboratory have demonstrated a significant reduction in the catalytic function of the 60 kDa and 63 kDa isozymes of calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) when comparing human cerebral tissue that was free of tumor and glioblastoma multiforme (GBM) and gliosarcoma [Lal S., Raju R. V. S., Macaulay R. B. J., and Sharma R. K. (1996) Can. J. Neurol. Sci., 23, 245-250]. The results suggested the possibility of an endogenously produced inhibitor of CaMPDE expressed in these tumors. Further investigation has initially characterized the presence of a heat-labile, protein inhibitor of both the 60 kDa and 63 kDa isozymes of CaMPDE. Sephacryl S-200 gel filtration column chromatography indicated that the inhibitor has an apparent molecular weight of 22 kDa and experimental evidence demonstrates that this inhibitor protein may act independently of calmodulin, and is therefore a novel CaMPDE inhibitor. Previous work on non-CNS tumors has shown high levels of CaMPDE activity and absence of an inhibitor. This suggests that a different mechanism may exist for the proliferation of these subsets of tumors.
Insights
Researchers identified a novel 22 kDa protein inhibitor of calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) in human brain tumors. This inhibitor may play a role in tumor growth, unlike in non-CNS tumors.
Area of Science:
- Biochemistry
- Neuroscience
- Oncology
Background:
- Previous studies showed reduced calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) activity in human glioblastoma multiforme (GBM) and gliosarcoma.
- This reduction suggested the presence of an endogenous CaMPDE inhibitor within these brain tumors.
Purpose of the Study:
- To characterize the endogenous inhibitor of CaMPDE found in human cerebral tumors.
- To determine the inhibitor's properties and its potential role in tumor proliferation.
Main Methods:
- Utilized Sephacryl S-200 gel filtration chromatography to estimate the molecular weight of the inhibitor.
- Performed experiments to assess the inhibitor's interaction with calmodulin and its effect on CaMPDE isozymes.
Main Results:
- Identified a heat-labile protein inhibitor with an apparent molecular weight of 22 kDa.
- Demonstrated that this novel inhibitor affects both 60 kDa and 63 kDa CaMPDE isozymes.
- Evidence suggests the inhibitor acts independently of calmodulin.
Conclusions:
- A novel 22 kDa CaMPDE inhibitor is present in human cerebral tumors.
- This inhibitor may contribute to the distinct mechanisms of proliferation in CNS tumors compared to non-CNS tumors.
- The inhibitor's calmodulin-independent action suggests a unique regulatory pathway in these cancers.