The maintenance of bone mass requires a strict balance between bone formation by osteoblasts and bone resorption by osteoclasts. In tumoral bone environment, tumor cells frequently disturb this balance by interaction with bone cells to create a favorable site for tumor growth, and promote pathological bone changes. Thus, elucidation of the mechanisms underlying interaction between tumor cells and bone cells might eventually lead to a more rational strategy for therapeutic intervention for bone tumors and better understanding of bone biology. In the present study, the effects of mouse osteosarcoma cells on mouse preosteoblastic cells were determined by assessment of cell viability, osteoblastic differentiation and signal transduction pathways. MOS-J/POS-1 conditioned media (CM) significantly induced MC3T3-E1 cell proliferation in a dose-dependent manner and reduced both alkaline phosphatase activity and mineralized nodule formation. Piceatannol, AG490, LY294002 and rapamycin significantly abrogated this up-regulated cell proliferation; however, UO126 and STAT3 inhibitor peptide did not affect this up-regulated cell proliferation. MOS-J/POS-1 CM activated ERK 1/2, STAT3 and Akt signal transduction pathways; however, pro-proliferating signal induced by MOS-J/POS-1 CM was transmitted via Akt not ERK 1/2 and STAT3 pathways. Furthermore, Western blot analyses clearly revealed novel signal crosstalk between JAKs and PI3-K/Akt in osteoblastic cells. The specific factor(s) involved in MOS-J/POS-1 CM-induced MC3T3-E1 cell proliferation that use JAKs/PI3-K/Akt/mTOR pathway remain(s) to be determined. Determination of the specific factor(s) responsible for JAKs and PI3-K/Akt signal crosstalk that results in up-regulated preosteoblast proliferation will offer new insight into the pathology of osteosarcoma as well as other bone-related diseases.