MAPK3 and osteosarcoma: In the clinical specimens from osteosarcoma patients, most chemotherapy-resistant specimens exhibited strong positive staining of p-FLNC, its kinase AKT1, and p-ERK1/2, a key protein in the ERK signaling cascade that regulates the growth and differentiation of cells; in contrast, the chemotherapy-sensitive specimens showed negative or weak positive staining of the above proteins (Additional file 5).