Alternative splicing of the proadrenomedullin gene results in differential expression of gene products

Abstract

The adrenomedullin (AM) gene codifies for two bioactive peptides, AM and proAM N-terminal 20 peptide (PAMP). We have found two forms of the AM mRNA. Form A is devoid of introns and results in a prohormone containing both peptides. Form B retains the third intron, which introduces a premature stop codon, producing a shorter prohormone with only PAMP. Tissues with a higher B/A ratio were more immunoreactive for PAMP than for AM. The form B message was found in the cytoplasmic compartment, thus excluding that the longer message was a result of contaminating nuclear mRNA. Form B was found in cells that express PAMP but not AM. mRNA expression in a variety of cell lines was investigated by ribonuclease protection assay and form B was found in significant amounts in two of them. Treatments that modify AM expression, such as exposure to hypoxia, were shown to change the B/A ratio and the relative secretion of AM and PAMP, indicating that the splicing mechanism for AM can be modulated and is physiologically relevant. Analysis of the sequence of the third intron and the fourth exon of the AM gene found motifs compatible with a highly regulated alternative splicing mechanism.

Changes and Distributions of Peptides Derived From Proadrenomedullin in Left-to-Right Shunt Pulmonary Hypertension of Rats

“…However, it has been demonstrated that hypoxia increases, whereas TNFdecreases, the B/A ratio. 17 Thus, secretion of proADMderived peptides may be regulated separately, which is reflected in the discrepancy of results for the distribution of ADM, ADT and PAMP in PHT. 18 Intramolecular regulation is defined as peptides originating from the same precursor and interacting with each other, 19 such as the cardiovascular bioactive peptides.…”

Proadrenomedullin NH2-Terminal 20 Peptide Is a Potent Angiogenic Factor, and Its Inhibition Results in Reduction of Tumor Growth

“…The expression of the adrenomedullin/PAMP gene during development is tightly regulated in a spatio-temporal manner (26), underscoring the need for a controlled liberation of these molecules. In addition, PAMP is rapidly degraded by neutral endopeptidases (27,28), resulting in extremely low levels of circulating PAMP (29). The silicone implant used in the directed in vivo angiogenesis assay may provide a secluded environment protecting PAMP from protease degradation, thus contributing to the angiogenic response observed at very low concentrations of PAMP.…”

“…Hypoxia is a common inducer of angiogenesis in tumors (31), and the adrenomedullin/PAMP gene is one of the many genes that is induced by low oxygen tension through a mechanism involving the transcription factor HIF-1 (32). Under hypoxic conditions, the alternative splicing mechanism of the gene favors the production of the longer mRNA species that produces PAMP but not adrenomedullin, thus increasing the relative amount of PAMP that is secreted from the cell (27). This regulatory mechanism is consistent with the angiogenic activity that we have described for PAMP.…”

Overexpression of adrenomedullin gene markedly inhibits proliferation of PC3 prostate cancer cells in vitro and in vivo

“…Although AM and PAMP are derived from the same precursor, they are not always expressed in the same cell types. A new splicing mechanism recently described may explain the differential distribution of AM and PAMP among organs and cell types (Martinez et al, 2001). Both AM and PAMP are present in plasma (Kitamura et al, 1994a;Washimine et al, 1994) and were initially described for their hypotensive activity and their ability to elevate cAMP (Kitamura et al, 1994b(Kitamura et al, , 1993a.…”