A protein phosphatase is a phosphatase enzyme that removes a phosphate group from the phosphorylated amino acid residue of its substrate protein. Protein phosphatases (PPs) are the primary effectors of dephosphorylation. In addition, Protein phosphatases can be grouped into three main classes based on sequence, structure and catalytic function. The largest class of PPs is the phosphoprotein phosphatase (PPP) family comprising PP1, PP2A, PP2B, PP4, PP5, PP6 and PP7, and PP2C.

Calyculin A (also known as (-)-Calyculin A) is a potent, selective and cell-permeable protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A) inhibitor. Calyculin A dephosphorylates serine and threonine residues in eukaryotic cells. Previously, Calyculin A induces contraction in smooth muscle fibers. In recent years, Hiroaki Tanaka et al. confirmed that Calyculin A can induce apoptosis in human osteoblastic cells. In addition, Calyculin A stimulates the expression of PTEN, FasL, and FasR mRNA in MG63 cells. Moreover, Calyculin A elicits phosphorylation of NF-κB on serine 536 in MG63 cells, resulting in the translocation of phospho-NF-κB to the nucleus, thereby promoting transcriptional activity of NF-κB-related genes.

Furthermore, Long-term 0.3 nM Calyculin A prevents G1 to S phase cell cycle progression in human Hs-68 fibroblasts and ARPE19 epithelial cells. However, acute application of 0.3 nM Calyculin A blocks serum-induced increase in intracellular calcium levels in Hs-68 fibroblasts.

In summary, Calyculin A is an natural, cell-permeable, selective serine-threonine protein phosphatases (PP) PP1 and PP2A inhibitor.


[1] Hiroaki Tanaka, et al. Int J Oncol. 2007 Aug;31(2):389-96.

[2] Maja Holy, et al. Toxins (Basel). 2012 Oct;4(10):940-54.