Influence of W-7, a calmodulin antagonist on phospholipid biosynthesis in Candida albicans

Rotavirus infection induces G1 to S phase transition in MA104 cells via Ca⁺²/Calmodulin pathway

Viruses, obligate cellular parasites rely on host cellular functions and target the host cell cycle for their own benefit. In this study, effect of rotavirus infection on cell cycle machinery was explored. We found that rotavirus (RV) infection in MA104 cells induces the expression of cyclins and cyclin dependent kinases and down-regulates expression of CDK inhibitors, resulting in G1 to S phase transition. The rotavirus induced S phase accumulation was found to be concurrent with induction in expression of calmodulin and activation of CaMKI which is reported as inducer of G1-S phase transition. This cell cycle manipulation was found to be Ca(+2)/Calmodulin pathway dependent. The physiological relevance of G1 to S phase transition was established when viral gene expressions as well as viral titers were found to be increased in S phase synchronized cells and decreased in G0/G1 phase synchronized cells compared to unsynchronized cells during rotavirus infection.

Identification of cellular calcium binding protein calmodulin as a regulator of rotavirus A infection during comparative proteomic study

Rotavirus (RV) being the major diarrhoegenic virus causes around 527000 children death (<5years age) worldwide. In cellular environment, viruses constantly adapt and modulate to survive and replicate while the host cell also responds to combat the situation and this results in the differential regulation of cellular proteins. To identify the virus induced differential expression of proteins, 2D-DIGE (Two-dimensional Difference Gel Electrophoresis) based proteomics was used. For this, HT-29 cells were infected with RV strain SA11 for 0 hours, 3 hours and 9 hours post infection (hpi), differentially expressed spots were excised from the gel and identified using MALDI-TOF/TOF mass spectrometry. 2D-DIGE based proteomics study identified 32 differentially modulated proteins, of which 22 were unique. Some of these were validated in HT-29 cell line and in BALB/c mice model. One of the modulated cellular proteins, calmodulin (CaM) was found to directly interact with RV protein VP6 in the presence of Ca²⁺. Ca²⁺-CaM/VP6 interaction positively regulates RV propagation since both CaM inhibitor (W-7) and Ca²⁺ chelator (BAPTA-AM) resulted in decreased viral titers. This study not only identifies differentially modulated cellular proteins upon infection with rotavirus in 2D-DIGE but also confirmed positive engagement of cellular Ca²⁺/CaM during viral pathogenesis.

Vitellogenesis in Oncopeltus fasciatus: PLC/IP(3), DAG/PK-C pathway triggered by CaM

In Oncopeltus fasciatus, evidence shown here indicates it is calmodulin (CaM) that activates phospholipase-C (PLC), beginning a signalling pathway necessary for endocytic uptake of yolk precursor molecules. Epithelial cell-produced CaM, transported to oocytes via gap junctions, has been shown to be required for receptor-mediated endocytic uptake of vitellogenins (Vgs, the protein precursors of yolk). To determine if CaM was directly or indirectly stimulating the phospholipase-C (PLC) signalling cascade and thus controlling Vg endocytosis we used a series of molecules known to inactivate various elements of the pathway. W-7 prevents CaM from interacting with other molecules. Neomycin isolates PIP(2) from PLC. U-73122 directly inactivates PLC. 2-APB blocks IP(3) receptors which would otherwise cause release of Ca(2+). Verapamil and CdCl(2) block Ca(2+) release channels. Staurosporin and calphostin are inhibitors of PK-C. 1-Hexadecyl-2-acetyl glycerol (HAG) binds to diacylglycerol (DAG). Through the use of these antagonists we show here that: (1) the activation of phospholipase-C in this system requires CaM. (2) Stimulated phospholipase-C converts PIP(2) into IP(3) and DAG. (3) IP(3) causes increase in cytosolic Ca(2+). (4) DAG and Ca(2+) each stimulate phosphokinase-C, resulting in endocytosis of Vgs.