This gene encodes a member of the RecA/Rad51-related protein family that participates inhomologous recombination to maintain chromosome stability and repair DNA damage. This gene functionally complements Chinese hamster irs1SF, a repair-deficient mutant that exhibits hypersensitivity to a number of different DNA-damaging agents and is chromosomally unstable. A rare microsatellite polymorphism in this gene is associated with cancer in patients of varying radiosensitivity.[6]
The XRCC3 protein is one of fiveparalogs ofRAD51, including RAD51B (RAD51L1), RAD51C (RAD51L2), RAD51D (RAD51L3),XRCC2 and XRCC3. They each share about 25% amino acid sequence identity with RAD51 and each other.[7]
The RAD51 paralogs are all required for efficient DNA double-strand break repair by homologous recombination and depletion of any paralog results in significant decreases in homologous recombination frequency.[8]
Two paralogs form a complex designated CX3 (RAD51C-XRCC3). Four paralogs form a second complex designated BCDX2 (RAD51B-RAD51C-RAD51D-XRCC2). These two complexes act at two different stages of homologous recombinationalDNA repair.
The CX3 complex acts downstream of RAD51, after its recruitment to damage sites.[8] The CX3 complex associates withHolliday junction resolvase activity, probably in a role of stabilizinggene conversion tracts.[8]
The BCDX2 complex is responsible for RAD51 recruitment or stabilization at damage sites.[8] The BCDX2 complex appears to act by facilitating the assembly or stability of theRAD51 nucleoprotein filament.
There is anepigenetic cause of XRCC3 deficiency that appears to increase cancer risk. This is the repression of XRCC3 by over-expression ofEZH2 protein.
Increased expression of EZH2 leads to epigenetic repression of RAD51 paralogs, including XRCC3, and thus reduceshomologous recombinational repair.[13] This reduction was proposed to be a cause of breast cancer.[13] EZH2 is the catalytic subunit of Polycomb Repressor Complex 2 (PRC2) which catalyzes methylation of histone H3 at lysine 27 (H3K27me) and mediates gene silencing of target genes via local chromatin reorganization.[14] EZH2 protein is up-regulated in numerous cancers.[14][15] EZH2 mRNA is up-regulated, on average, 7.5-fold in breast cancer, and between 40% and 75% of breast cancers have over-expressed EZH2 protein.[16]
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Price EA, Bourne SL, Radbourne R, Lawton PA, Lamerdin J, Thompson LH, Arrand JE (1998). "Rare microsatellite polymorphisms in the DNA repair genes XRCC1, XRCC3 and XRCC5 associated with cancer in patients of varying radiosensitivity".Somat. Cell Mol. Genet.23 (4):237–247.doi:10.1007/BF02674415.PMID9542526.S2CID32956047.
Winsey SL, Haldar NA, Marsh HP, Bunce M, Marshall SE, Harris AL, Wojnarowska F, Welsh KI (2000). "A variant within the DNA repair gene XRCC3 is associated with the development of melanoma skin cancer".Cancer Res.60 (20):5612–6.PMID11059748.
Duan Z, Shen H, Lee JE, Gershenwald JE, Ross MI, Mansfield PF, Duvic M, Strom SS, Spitz MR, Wei Q (2002). "DNA repair gene XRCC3 241Met variant is not associated with risk of cutaneous malignant melanoma".Cancer Epidemiol. Biomarkers Prev.11 (10 Pt 1):1142–3.PMID12376526.
Smith TR, Miller MS, Lohman K, Lange EM, Case LD, Mohrenweiser HW, Hu JJ (2003). "Polymorphisms of XRCC1 and XRCC3 genes and susceptibility to breast cancer".Cancer Lett.190 (2):183–190.doi:10.1016/S0304-3835(02)00595-5.PMID12565173.
Jacobsen NR, Nexø BA, Olsen A, Overvad K, Wallin H, Tjønneland A, Vogel U (2004). "No association between the DNA repair gene XRCC3 T241M polymorphism and risk of skin cancer and breast cancer".Cancer Epidemiol. Biomarkers Prev.12 (6):584–5.PMID12815008.
Zhu G, Duffy DL, Turner DR, Ewen KR, Montgomery GW, Martin NG (2005). "Linkage and association analysis of radiation damage repair genes XRCC3 and XRCC5 with nevus density in adolescent twins".Twin Research.6 (4):315–321.doi:10.1375/136905203322296683.hdl:2328/10191.PMID14511439.
