PMS2

Mismatch repair endonuclease PMS2 is an is_associated_with::enzyme that in humans is encoded by the PMS2 is_associated_with::gene.

Function
This gene is one of the PMS2 gene family members which are found in clusters on chromosome 7. Human PMS2 related genes are located at bands 7p12, 7p13, 7q11, and 7q22. Exons 1 through 5 of these homologues share high degree of identity to human PMS2 The product of this gene is involved in is_associated_with::DNA mismatch repair. The protein forms a heterodimer with is_associated_with::MLH1 and this complex interacts with is_associated_with::MSH2 bound to mismatched bases. Defects in this gene are associated with is_associated_with::hereditary nonpolyposis colorectal cancer, with is_associated_with::Turcot syndrome, and are a cause of supratentorial is_associated_with::primitive neuroectodermal tumors. Alternatively spliced transcript variants have been observed.

Mismatch repair and endonuclease activity
PMS2 is involved in mismatch repair and is known to have latent is_associated_with::endonuclease activity that depends on the integrity of the meta-binding motif in MutL homologs. As an endonuclease, PMS2 introduces nicks into a discontinous DNA strand.

Mutations
PMS2 is a gene that encodes for DNA repair proteins involved in is_associated_with::mismatch repair. The PMS2 gene is located on chromosome 7p22 and it consists of 15 exons. Exon 11 of the PMS2 gene has a coding repeat of eight adenosines.

Heterozygous germline mutations in DNA mismatch repair genes like PMS2 lead to autosomal dominant Lynch syndrome. Only 2% of families that have Lynch syndrome have mutations in the PMS2 gene. The age of patients when they first presented with PMS2-associated Lynch syndrome varies greatly, with a reported range of 23 to 77 years.

In rare cases, a homozygous defect may cause this syndrome. In such cases a child inherits the gene mutation from both parents and the condition is called Turcot syndrome or Constitutional MMR Deficiency (CMMR-D). Up until 2011, 36 patients with brain tumors due to biallelic PMS2 germline mutations have been reported. Inheritance of Turcot syndrome can be dominant or recessive. Recessive inheritance of Turcot syndrome is caused by compound heterozygous mutations in PMS2. 31 out of 57 families reported with CMMR-D have germline PMS2 mutations. 19 out of 60 PMS2 homozygous or compound heterozygous mutation carriers had gastrointestinal cancer or adenomas as the first manifestation of CMMR-D. Presence of pseudogenes can cause confusion when identifying mutations in PMS2, leading to false positive conclusions of the presence of mutated PMS2.

Deficiency and overexpression
Overexpression of PMS2 results in hypermutability and DNA damage tolerance. Deficiency of PMS2 also contributes to genetic instability by allowing for mutations to propagate due to reduced MMR function. It has been shown that PMS2-/- mice developed lymphomas and sarcomas. It was also shown that male mice that are PMS2-/- are sterile, indicating that PMS2 may have a role in spermatogenesis.

Interactions
PMS2 has been shown to interact with is_associated_with::MLH1 by forming the heterodimer MutLα. There is competition between MLH3, PMS1, and PMS2 for the interacting domain on MLH1, which is located in residues 492-742.

The interacting domains in PMS2 have heptad repeats that are characteristic of leucine zipper proteins. MLH1 interacts with PMS2 at residues 506-756.

The MutS heterodimers, MutSα and MutSβ, associate with MutLα upon mismatch binding. MutLα is believed to join the mismatch recognition step to other processes, including: removal of mismatches from the new DNA strand, resynthesis of the degraded DNA, and repair of the nick in the DNA. MutLα is shown to have weak ATPase activity and also possesses endonuclease activity that introduces nicks into the discontinuous strand of DNA. This facilitates 5' to 3' degradation of the mismatched DNA strand by EXO1. The active site of MutLα is located on the PMS2 subunit. PMS1 and PMS2 compete for interaction with MLH1. Cannavo et al. list some of the proteins in the interactome of PMS2 identified by tandem affinity purification.

Human PMS2 is expressed at very low levels and is not believed to be strongly cell cycle regulated.

Interactions involving p53 and p73
PMS2 has also been shown to interact with is_associated_with::p53 and is_associated_with::p73. In the absence of p53, PMS2-deficient and PMS2-proficient cells are still capable of arresting the cell cycle at the G2/M checkpoint when treated with is_associated_with::cisplatin. Cells that are deficient in p53 and PMS2, exhibit increased sensitivity to anticancer agents. PMS2 is a protective mediator of cell survival in p53-deficient cells and modulates protective DNA damage response pathways independently of p53. PMS2 and MLH1 can protect cells from cell death by counteracting p73-mediated apoptosis in a mismatch repair dependent manner.

PMS2 can interact with p73 to enhance cisplatin-induced apoptosis by stabilizing p73. Cisplatin stimulates the interaction between PMS2 and p73, which is dependent on c-Abl. The MutLα complex may function as an adapter to bring p73 to the site of damaged DNA and also act as an activator of p73, due to the presence of PMS2. It may also be possibly for overexpressed PMS2 to stimulate apoptosis in the absence of MLH1 and in the presence of p73 and cisplatin due to the stabilizing actions of PMS2 on p73. Upon DNA damage, p53 induces cell cycle arrest through the is_associated_with::p21/WAF pathway and initiates repair by expression of MLH1 and PMS2. The MSH1/PMS2 complex acts as a sensor of the extent of the damage to the DNA, and initiates apoptosis by stabilizing p73 if the damage is beyond repair. Loss of PMS2 does not always lead to instability of MLH1 since it can also form complexes with MLH3 and PMS1.