Forty-five years of cGMP research in Dictyostelium: understanding the regulation and function of the cGMP pathway for cell movement and chemotaxis.

In Dictyostelium, chemoattractants induce a fast cGMP response that mediates myosin filament formation in the rear of the cell. The major cGMP signaling pathway consists of a soluble guanylyl cyclase sGC, a cGMP-stimulated cGMP-specific phosphodiesterase, and the cGMP-target protein GbpC. Here we combine published experiments with many unpublished experiments performed in the past 45 years on the regulation and function of the cGMP signaling pathway. The chemoattractants stimulate heterotrimeric Gαßγ and monomeric Ras proteins. A fraction of the soluble guanylyl cyclase sGC binds with high affinity to a limited number of membrane binding sites, which is essential for sGC to become activated by Ras and Gα proteins. sGC can also bind to F-actin; binding to branched F-actin in pseudopods enhances basal sGC activity, whereas binding to parallel F-actin in the cortex reduces sGC activity. The cGMP pathway mediates cell polarity by inhibiting the rear: in unstimulated cells by sGC activity in the branched F-actin of pseudopods, in a shallow gradient by stimulated cGMP formation in pseudopods at the leading edge, and during cAMP oscillation to erase the previous polarity and establish a new polarity axis that aligns with the direction of the passing cAMP wave.

Identification and characterization of the V3 promoter of the ST3GAL4 gene.

The ST3GAL4 gene encodes the enzyme Galß1-4GlcNAc α2,3 sialyltransferase (ST3Gal IV). This enzyme participates in the synthesis of the sialyl Lewis x antigen. In different cancer types altered expression of this antigen has been reported. The transcriptional regulation of this gene is very complex, different mRNA variants (V1-V10) have been reported and are originated by the activity of different promoters and alternative splicing. Only the promoter that gives rise to the V3 variant has not been previously reported. The objective of this work was to identify and characterize the V3 promoter of the ST3GAL4 gene. For this, the putative V3 promoter of the ST3GAL4 gene was delimited by in silico analysis. The complete promoter and smaller versions were cloned in a reporter plasmid. The constructs were transfected in the HaCaT cells and the promoter activity was evaluated by luciferase reporter assays. The cloned region showed promoter activity, and the basal activity was not dependent on TATA boxes. However, the GC boxes, an initiator element (Inr) and downstream promoter element (DPE) could contribute to basal activity. The promoter contains several binding sites for the nuclear factor of activated T-cells (NFAT) that could participate in inducible activity during the immune response. The minimal promoter corresponds to a fragment of approximately 300 bp, located in the position -347 b to -40 b. The characterization of the V3 promoter of the ST3GAL4 gene completes the study of the four promoters of this gene, this contributes to the understanding of its complex transcription regulation.

Expression analysis of ST3GAL4 transcripts in cervical cancer cells.

ST3GAL4 gene expression is altered in different cancer types, including cervical cancer. Several mRNA transcripts have been reported for this gene; however, their expression levels in cervical cancer have not been analyzed. ST3GAL4 encodes for ß­galactosidase α­2,3­sialyltransferase 4, involved in the biosynthesis of the tumour antigens sLe(x) and sulfo­sLe(x). The present study evaluated the presence of three mRNA variants (V1, V2 and V3) in cervical cancer cell lines, detecting the three variants. Additionally, the expression level of the V1 transcript of the ST3GAL4 gene was determined by reverse transcription­quantitative polymerase chain reaction in cervical cell lines and in normal, premalignant and cervical cancer tissue. The V1 transcript of the ST3GAL4 demonstrated significant decreased expression in premalignant and malignant cervical tissues. The results suggested that deregulation of this gene could occur prior to the presence of cancer and demonstrated the importance of evaluating the expression level of V1, and its association with disease progression.