Osteosarcoma is the most frequent primary malignant bone
tumor among the children. The advent of
neoadjuvant chemotherapy significantly improved the prognosis of patients with
osteosarcoma in the 1980s, but it has since plateaued in the past decades. Recently, one of the most researched areas in
sarcoma treatment is
tyrosine kinases. Here, we describe research on a
serine/threonine kinase,
cyclin G-associated
kinase (GAK), which has not been reported in
osteosarcoma previously. In this study, a lentiviral based human
shRNA library was utilized to screen for
kinases in KHOS and U-2OS
osteosarcoma cells. The expression of GAK was examined in
osteosarcoma and the effect on cell proliferation was analyzed by GAK
siRNA knockdown. The level of GAK expression and its correlation to prognosis was analyzed in
osteosarcoma tissue microarray. The effect of GAK depletion on
insulin-like growth factor and
epidermal growth factor receptor-mediated signal transduction was analyzed by Western blot. We observed that GAK was overexpressed in both
osteosarcoma cell lines and tissue samples when compared with human osteoblasts. GAK knockdown by
siRNA decreased cell proliferation in both
drug-sensitive and multidrug-resistant
osteosarcoma cell lines. Immunohistochemistry of
osteosarcoma tissue microarray revealed that overexpression of GAK was associated with poor prognosis. Finally, knockdown of GAK resulted in alterations of receptor trafficking and several downstream
proteins. In conclusion, our results suggest that
osteosarcoma cell proliferation and survival are dependent on GAK. These findings may lead to the development of new therapeutic options for
osteosarcoma.