Identification of Lynch syndrome mutations in the MLH1-PMS2 interface that disturb dimerization and mismatch repair

Abstract

Missense alterations of the mismatch repair gene MLH1 have been identified in a significant proportion of individuals suspected of having Lynch syndrome, a hereditary syndrome that predisposes for cancer of colon and endometrium. The pathogenicity of many of these alterations, however, is unclear. A number of MLH1 alterations are located in the C-terminal domain (CTD) of MLH1, which is responsible for constitutive dimerization with PMS2. We analyzed which alterations may result in pathogenic effects due to interference with dimerization. We used a structural model of CTD of MLH1-PMS2 heterodimer to select 19 MLH1 alterations located inside and outside two candidate dimerization interfaces in the MLH1-CTD. Three alterations (p.Gln542Leu, p.Leu749Pro, p.Tyr750X) caused decreased coexpression of PMS2, which is unstable in the absence of interaction with MLH1, suggesting that these alterations interfere with dimerization. All three alterations are located within the dimerization interface suggested by our model. They also compromised mismatch repair, suggesting that defects in dimerization abrogate repair and confirming that all three alterations are pathogenic. Additionally, we provided biochemical evidence that four alterations with uncertain pathogenicity (p.Ala586Pro, p.Leu636Pro, p.Thr662Pro, and p.Arg755Trp) are deleterious because of poor expression or poor repair efficiency, and confirm the deleterious effect of eight further alterations. Hum Mutat 31:975-982,

The Germline MLH1 K618A Variant and Susceptibility to Lynch Syndrome-Associated Tumors

“…Guerrette et al 43 45 Bianchi et al, 29 and Kosinski et al 46 found normal MLH1-PMS2 in vitro binding activity in their studies. Raevaara et al 45 also performed other in vitro MLH1 protein functional studies, including protein expression and stability, subcellular localization, protein-protein interaction, and repair efficiency.…”

“…The first three studies (Guerrette et al, 43 Kondo et al, 44 and Belvederesi et al 28 ) show that the K618A variant has substantially lower ability to bind PMS2, but that it still binds a nontrivial fraction of the available PMS2. The studies by Raevaara et al 45 and Kosinski et al, 46 however, showed no difference between K618A and wild-type MLH1 constructs with respect to PMS2 binding. The Raevaara group used a method quite different from those of the other four studies, one that may not be able to distinguish between normal and reduced binding.…”

“…Although K618 is often described as being in the PMS2 binding domain (eg, Figure 2 in Chao et al 2008 52 ), this more detailed model shows that position 618 is not directly involved in PMS2 binding. 46 Raevaara et al 45 used a somewhat different experimental design. They coexpressed mutant MLH1 and wild-type PMS2 from baculovirus constructs in Sf9 cells.…”

A founder MLH1 mutation in Lynch syndrome families from Piedmont, Italy, is associated with an increased risk of pancreatic tumours and diverse immunohistochemical patterns

“…It has been previously reported that terminal MLH1 defects prevent the formation of a stable complex with PMS2, resulting in an impaired DNA mismatch repair function [6,9]. Although dimerization is not required for nuclear localization, the MLH1-PMS2 heterodimer is imported in the nucleus more efficiently than either MLH1 or PMS2 monomers [57].…”

“…Germline mutations in MLH1 have been identified throughout the entire gene, and are frequently located in the ATP binding domain and in the C-terminal region which is responsible for constitutive dimerization with the PMS2 protein [6][7][8][9].…”