PTP1B is a tyrosine-protein phosphatase which acts as a regulator of endoplasmic reticulum unfolded protein response and mediates dephosphorylation of EIF2AK3/PERK, inactivating the protein kinase activity of EIF2AK3/PERK. During metaphase, PTP1B is phosphorylated by protein kinase C (PKC) at S352, which is also phosphorylated in response to osmotic stress, but do not markedly change PTP1B activity.
