Induction of two DNA mismatch repair proteins, MSH2 and MSH6, in differentiated human neuroblastoma SH-SY5Y cells exposed to doxorubicin

The MutS homologues MSH2 and MSH6 form a heterodimeric protein complex that is involved in the recognition of base/base mismatches and insertion/delet ion loops, as well as some other types of DNA damage. We investigated the e xpression of these proteins in undifferentiated and retinoic acid-different iated human neuroblastoma SH-SY5Y cells by immunocytochemistry, western blo t analysis, and RT-PCR. Nuclei from undifferentiated SH-SY5Y cells were fou nd to be immunoreactive to anti-MSH2 and anti-MSH6 antibodies. Following di fferentiation, the cells stop dividing and change morphology to acquire a n euron-like phenotype. Under these conditions, both anti-MSH2 and anti-MSH6 immunoreactivities were still detectable, although the signals were somewha t less intense. When these cells were exposed for 2 h to neurotoxic concent rations of doxorubicin (50 nM), they exhibited a marked and homogeneous inc rease of both anti-MSH2 and anti-MSH6 immunoreactivities. As revealed by we stern blot analysis, these effects were associated with increased protein c ontent and were dose-dependent. Using RT-PCR technology, we also found that doxorubicin treatment did not change MSH2 or MSH6 mRNA levels. Our data in dicate that human postmitotic, neuron-like cells constitutively express the molecular machinery devoted to recognition of DNA mismatches and that this system is activated by specific treatment leading to cell death. These fin dings might help clarify the molecular mechanisms underlying various human neurological diseases that are associated with deficiencies in DNA repair a nd/or a high rate of DNA damage acquisition.