Ganglioside GD1a has been reported to suppress metastasis [S. Hyuga, S. Yamagata, Y. Takatsu, M. Hyuga, H. Nakanishi, K. Furukawa, T. Yamagata, Suppression of FBJ-LL cell adhesion to vitronectin by ganglioside GD1a and loss of metastatic capacity, International J. Cancer. 83 (1999) 685-691.] and MMP-9 production in mouse osteosarcoma FBJ cells [D. Hu, Z. Man, P. Wang, X. Tan, X Wang, S. Takaku, S. Hyuga, T. Sato, X Yao, S. Yamagata, T. Yamagata, Ganglioside GD1a negatively regulates MMP9 expression in mouse FBJ cell lines at the transcriptional level, Connect. Tissue Res. 48 (2007) 198-205.]. In the present study, TNF alpha. increased cell motility and MMP-9 and TNF alpha expression at the transcriptional level. TNF alpha expression was found to be inversely proportional to GD1a content in the FBJ-cell variants. The addition of exogenous GD1a to FBJ-LL cells suppressed TNF alpha expression, and treatment of FBJ-S1 cells with D-PDMP (glucosylceramide synthesis inhibitor) led to an increase in TNF alpha, indicating that TNF alpha is negatively regulated by GD1a in FBJ cells. SiRNA of Pkn1, a Rho-GTPase effecter protein kinase, suppressed TNF alpha levels as well as Pkn1 expression, suggesting that Pkn1 is involved in TNF alpha signaling. Treatment of Pkn1-silenced FBJ-LL cells with GD1a failed to suppress TNF alpha expression, demonstrating that GD1a signals that lead to TNF alpha suppression are transduced through Pkn1. (C) 2008 Elsevier Inc. All rights reserved.