Cytotoxic Necrotizing Factor 1 (CNF1) is a
protein toxin from Escherichia coli that constitutively activates the Rho, Rac and Cdc42
GTPases. These regulatory
proteins oscillate between a cytosolic
GDP-bound inactive form and a membrane-linked
GTP-bound active form, orchestrating the actin cytoskeleton assembly and dynamics. We herein describe, for the first time, the ability of CNF1 to potently counteract the
formalin-induced inflammatory
pain in mice. The
analgesic response due to CNF1 requires both the sustained activation of the Rac
GTPase, with consequent cerebral actin cytoskeleton remodeling, and the up-regulation of the
mu-opioid receptors (MORs), the most important receptors controlling pain perception. The crucial role of Rac is proved by the lack of
analgesic activity in mice challenged with a recombinant CNF1, in which the enzymatic activity was abolished by substituting
serine with
cysteine at position 866. The importance of MORs is proved by the inability of CNF1 to induce any
analgesic effect in MORs knockout mice and by the ability of
naloxone to antagonize the
analgesic effects. Furthermore, it is worth noting that the
analgesic effect in mice occurs after both peripheral and central administration of CNF1. Hence, taken altogether, our findings provide new insights into the comprehension of intracellular mechanisms involved in
pain modulation, and indicate this
bacterial protein toxin as a novel tool in the field of
pain control. Conceivably, this might pave the way for new therapeutic strategies.