PIWIL1 and Miyoshi myopathy: To investigate whether PIWIL1 promotes MM cell growth to acquire malignant/progressive traits, we used lentiviral transfection to stably establish the PIWIL1-overexpressing MM cell lines PIWIL1+ 8226 and PIWIL1+ 929; the PIWIL1-downregulated MM cell lines PIWIL1– 8226 and PIWIL1– 929; and their negative controls, PIWIL1+ 8226 NC, PIWIL1+ 929 NC, PIWIL1– 8226 NC, and PIWIL1– 929 NC.