Calponin 2

[30] Significant amounts of calponin 2 are found in growing smooth muscle tissues such as embryonic stomach and urinary bladder as well as the uterus during early pregnancy.

[6][14] A hypothesis is that higher level of calponin 2 is required in fast proliferating cells to maintain the dynamic equilibrium of the actin cytoskeleton.

Primary fibroblasts and peritoneal macrophages isolated from Cnn2 knockout mice migrate faster than that of wild type control cells.

In a microfluidic flow-based thrombosis assay, the time to initiation of rapid platelet/thrombus accumulation was significantly longer in blood samples from Cnn2 knockout versus wild type mice.

[8] The expression of calponin 2 in NIH/3T3 cells was decreased when cytoskeleton tension was reduced after blebbistatin inhibition of myosin II motors.

[9] To demonstrate the Cnn2 promoter-specific regulation, transfective expression of calponin 2 using a cytomegalovirus promoter was independent of the stiffness of culture substrate.

[8] A binding site for transcriptional factor HES-1 (hairy and enhancer of split 1) has been identified in the 5’-upstream region of mouse Cnn2 promoter, responsible for the mechanical regulation.

[32][33] Deletion or mutation of the HES-1 site abolished the mechanical regulation and resulted in a substrate stiffness independent high level of transcription.

Figure 1: Evolutionary lineage of vertebrate calponin 2 deduced from alignment of amino acid sequences.
Figure 2. Proteins interacting with calponin. Calponin binds actin filaments through two actin-binding sites (ABS1 and ABS2), tropomyosin via the N-terminal CH domain, and gelsolin via the region of actin-binding sites. Calponin interacts with microtubules through the region including the actin-binding sites and the repeating motifs and with desmin through the region from N-terminal domain to the end of actin-binding sites. The segment of amino acids 144-182 in calponin interacts with myosin. In the presence of Ca 2+ , calmodulin and S100 bind calponin at the region of actin-binding sites and reverse calponin’s inhibition of myosin MgATPase. An N-terminal 22-kDa fragment of calponin interacts with phosphatidylserine and phosphatidylinositol. *The interaction between calponin and caldesmon is controversial.