Nuclear factor-κB activation by the CXC chemokine melanoma growth-stimulatory activity/growth-regulated protein involves the MEKK1/p38 mitogen-activated protein kinase pathway

Melanoma growth stimulatory activity/growth-regulated protein (MGSA/GRO), a CXC chemokine, plays an important role in inflammation, wound healing, growth regulation, angiogenesis, and tumorigenesis, Constitutive expression of MGSA/GRO alpha in melanoma tumors is associated with constitutive nuclear factor (NF)-kappaB activity. We show here that either exogenous addition or continuous expression of MGSA/GRO alpha in immortalized melanocytes enhances NF-kappaB activation, as well as mitogen-activated protein (MAP) kinase kinase kinase (MEKK) 1, MAP kinase kinase (MEK) 3/6, and p38 MAP kinase activation. Expression of dominant negative MRas (S27N), dominant negative MEKK1 (K432M), or specific chemical inhibitors for p38 MAP kinase (SB202190 and SB203580) block MGSA/GRO alpha -induced NF-kappaB transactivation, demonstrating that Pas, MEKK1, and p38 are involved in the signal pathways of MGSA/GRO alpha activation of NF-kappaB, Expression of dominant active Res or dominant active MEKK1 alone can also stimulate NF-kappaB activation. The expression of dominant negative MEKK1 inhibits the Pas-induced NF-kappaB activation, suggesting that MEKK1 is a downstream target of Pas, Moreover, MGSA/GRO alpha induction of NF-kappaB is independent of the MEK1/ERK cascade, because MGSA/GRO alpha failed to increase ERK and ELK activation, and specific chemical inhibitors for MEK1 (PD98059) had no effect on MGSA/GRO alpha -enhanced NF-kappaB activation. These data demonstrate that NF-kappaB activation is required for MGSA/GRO alpha -induced melanocyte transformation through a Ras/MEKK1/p38 cascade in melanocytes.