The Human DNA Mismatch Repair Protein MSH3 Contains Nuclear Localization and Export Signals That Enable Nuclear-Cytosolic Shuttling in Response to Inflammation

Abstract

Inactivation of DNA mismatch repair propels colorectal cancer (CRC) tumorigenesis. CRCs exhibiting elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) show reduced nuclear MutS homolog 3 (MSH3) expression with surrounding inflammation and portend poor patient outcomes. MSH3 reversibly exits from the nucleus to the cytosol in response to the proinflammatory cytokine interleukin-6 (IL-6), suggesting that MSH3 may be a shuttling protein. In this study, we manipulated three putative nuclear localization (NLS1 to -3) and two potential nuclear export signals (NES1 and -2) within MSH3. We found that both NLS1 and NLS2 possess nuclear import function, with NLS1 responsible for nuclear localization within full-length MSH3. We also found that NES1 and NES2 work synergistically to maximize nuclear export, with both being required for IL-6-induced MSH3 export. We examined a 27-bp deletion (Δ27bp) within the polymorphic exon 1 that occurs frequently in human CRC cells and neighbors NLS1. With oxidative stress, MSH3 with this deletion (Δ27bp MSH3) localizes to the cytoplasm, suggesting that NLS1 function in Δ27bp MSH3 is compromised. Overall, MSH3’s shuttling in response to inflammation enables accumulation in the cytoplasm; reduced nuclear MSH3 increases EMAST and DNA damage. We suggest that polymorphic sequences adjacent to NLS1 may enhance cytosolic retention, which has clinical implications for inflammation-associated neoplastic processes.

Fusobacterium nucleatum infection correlates with two types of microsatellite alterations in colorectal cancer and triggers DNA damage

“…These observations might suggest that Fn infection may contribute to a serrated pathway of CRC development [ 4 ]. On the other hand, tumor tissue infected with Fn exhibits an inflamed tumor microenvironment, rich in inflammatory factors such as IL6 or reactive oxygen species [ 5 ], leading to the assumption that Fn infection might also contribute to the generation of IAMA or L/E positive CRC [ 6 – 8 ]. Despite a strong association between Fn infection and colorectal cancer, there has been no evidence of Fn infection damaging the DNA of colon tissues.…”

HDAC3 deacetylates the DNA mismatch repair factor MutSβ to stimulate triplet repeat expansions

“…4 A ). Another group recently reported NLS activity in this same Msh3 motif ( 69 ). They showed that the strongest NLS in Msh3 is between residues 84 and 107, with particular requirement for the region 98 to 107.…”

“…One outcome of HDAC3 action is to partially control the nuclear localization of MutSβ. Immunofluorescence microscopy and subcellular localization approaches revealed that the deacetylation sites in Msh3 overlap a nuclear localization signal (69). Cells expressing wild-type Msh3 sequences showed nuclear localization that was reduced, although not eliminated, by addition of RGFP966.…”

“…4A) showed that Msh3 lysine residues 98 and 99 align with part of the NLS from Msh6, and that Msh3 lysine 103 also aligns with a cognate lysine in Msh6. The putative NLS in Msh3 overlaps with a strong functional NLS between residues 98 and 107 of Msh3 that was recently described (69). We sought to build on this knowledge with experiments to test the possibility that the acetylation status of lysine residues in the predicted Msh3 NLS controls the subcellular localization of Msh3 and thereby helps regulate triplet repeat expansions.…”

Role of mismatch repair in aging

“…After UV-B induced DNA damage, the MMR system promoted G2/M phase arrest [166]. MSH3 accumulates in the cytoplasm due to its shuttle response to inflammation; reduced nucleoprotein MSH3 increases EMAST (elevated microsatellite alterations at selected tetranucleotide) and DNA damage [167]. The MMR pathway is also of particular interest in neurodegenerative diseases because of its influence on somatic amplification of CAG repeats, which increase in length over time, especially in the brain [168].…”