Neisseria gonorrhoeae andNeisseria meningitidis are Gram-negative bacterial pathogens that infect human mucosal epithelia. Type IV pilus-mediated adherence of these bacteria is a crucial early event for establishment of infection. In this work, we show that the type IV pili transduce a signal into the eucaryotic host cell. Purified adherent pili, but not pili from a low binding mutant, trigger an increase in the cytosolic free calcium ([Ca²⁺]_i) in target epithelial cells, a signal known to control many cellular responses. The [Ca²⁺]_i increase was blocked by antibodies against CD46, a putative pilus receptor, suggesting a role for this protein in signal transduction. Pilus-mediated attachment was inhibited by depletion of host cell intracellular Ca²⁺ stores but not by removal of extracellular Ca²⁺. Further, kinase inhibition studies showed that pilus-mediated adherence is dependent on casein kinase II. In summary, these data reveal a novel function of the type IV pili, namely induction of signal transduction pathways in host cells.

Molecular mechanisms that regulatein situactivation of ryanodine receptors (RY) in different cells are poorly understood. Here we demonstrate that caffeine (10 mM) released Ca²⁺from the endoplasmic reticulum (ER) in the form of small spikes in only 14% of cultured fura-2 loaded beta cells fromob/obmice. Surprisingly, when forskolin, an activator of adenylyl cyclase was present, caffeine induced larger Ca²⁺spikes in as many as 60% of the cells. Forskolin or the phosphodiesterase-resistant PKA activator Sp-cAMPS alone did not release Ca²⁺from ER. 4-Chloro-3-ethylphenol (4-CEP), an agent that activates RYs in other cell systems, released Ca²⁺from ER, giving rise to a slow and small increase in [Ca²⁺]_iin beta cells. Prior exposure of cells to forskolin or caffeine (5 mM) qualitatively altered Ca²⁺release by 4-CEP, giving rise to Ca²⁺spikes. In glucose-stimulated beta cells forskolin induced Ca²⁺spikes that were enhanced by 3,9-dimethylxanthine, an activator of RYs. Analysis of RNA from islets and insulin-secreting βTC-3-cells by RNase protection assay, using type-specific RY probes, revealed low-level expression of mRNA for the type 2 isoform of the receptor (RY₂). We conclude thatin situactivation of RY₂in beta cells requires cAMP-dependent phosphorylation, a process that recruits the receptor in a functionally operative form.