Ca2+differently affects hydrophobic properties of guanylyl cyclase-activating proteins (GCAPs) and recoverin.

Guanylyl cyclase-activating proteins (GCAPs) and recoverin are retina-specific Ca2+-binding proteins involved in phototransduction. We provide here evidence that in spite of structural similarities GCAPs and recoverin differently change their overall hydrophobic properties in response to Ca2+. Using native bovine GCAP1, GCAP2 and recoverin we show that: i) the Ca2+-dependent binding of recoverin to Phenyl-Sepharose is distinct from such interactions of GCAPs; ii) fluorescence intensity of 1-anilinonaphthalene-8-sulfonate (ANS) is markedly higher at high [Ca2+]gfree (10 μM) than at low [Ca2+]free (10 nM) in the presence of recoverin, while an opposing effect is observed in the presence of GCAPs; iii) fluorescence resonance energy transfer from tryptophane residues to ANS is more efficient at high [Ca2+]free in recoverin and at low [Ca2+]free in GCAP2. Such different changes of hydrophobicity evoked by Ca2+ appear to be the precondition for possible mechanisms by which GCAPs and recoverin control the activities of their target enzymes

Sp1 mediates phorbol ester (PMA)-induced expression of membrane-bound guanylyl cyclase GC-A in human monocytic THP-1 cells

Cyclic guanosine monophosphate (cGMP) is synthesized by two types of enzymes: particulate (membrane-bound) guanylyl cyclases (pGCs) and soluble (cytosolic) guanylyl cyclases (sGCs). sGCs are primarily activated by binding of nitric oxide to their prosthetic heme group while pGCs are activated by binding of peptide ligands to their extracellular domains. One of them, pGC type A (GC-A) is activated by atrial and brain natriuretic peptides (ANP and BNP, respectively). Human monocytes isolated from peripheral blood mononuclear cells have been found to display sGC expression without concomitant expression of GC-A. However, GC-A activity appears in monocytes under certain conditions but a molecular mechanism of GC-A expression is still poorly understood. In this report we show that phorbol ester (PMA) induces transcription of a gene encoding GC-A in human monocytic THP-1 cells. Moreover, we find that PMA-treated THP-1 cells raise cGMP content following treatment with ANP. Studies using pharmacological inhibitors of protein kinases suggest involvement of protein kinase C (PKC), mitogen extracellular kinases (MEK1/2), and extracellular signal-regulated kinases (ERK1/2) in PMA-induced expression of the GC-A encoding gene in THP-1 cells. Finally, we show that PMA stimulates binding of Sp1 transcription factor to GC-rich DNA sequences and mithramycin A (a selective Sp1 inhibitor) inhibits expression of the GC-A mRNA in PMA-treated THP-1 cells. Taken together, our findings suggest that the PMA-stimulated PKC and MEK/ERK signaling pathways induce Sp1-mediated transcription of the GC-A encoding gene in human monocytic THP-1 cells