Degradation of cellular mRNA is a general early apoptosis‐induced event

Abstract

The fate of cellular mRNAs was analyzed in several cell lines of lymphoid origin, after induction of apoptosis by different mechanisms. Cytoplasmic mRNAs are specifically degraded as part of the early apoptotic response. This degradation is not species restricted and is independent of the cell line, the apoptotic stimulus, the intrinsic half-life of the mRNAs, and the transcriptional status of the gene (constitutive or inducible). mRNA degradation precedes DNA fragmentation and correlates with the appearance of phosphatidylserine in the outer cell membrane. In addition, apoptosis-induced mRNA degradation is an active process that can be dissected from other apoptotic hallmarks (degradation of annexin V, DNA, and poly(ADP-ribose) polymerase [PARP]), which suggests that apoptosis-induced mRNA degradation is controlled by a distinct signaling pathway. Furthermore, mRNA degradation also occurs in vivo, specifically during thymocyte apoptosis. Taken together, these data support the notion that degradation of mRNA is a general early apoptotic event that may become a new apoptotic hallmark.Key words: RNA metabolism • caspase inhibitors • signaling pathways • in vivo apoptosis T he genetically programmed cell death process known as apoptosis is fundamental for the normal development and homeostasis of tissues and organs in multicellular organisms.The relevance of apoptosis is demonstrated both by the evolutionary conservation of basic steps in the corresponding pathways (1) and by the causal implication of aberrant apoptotic mechanisms in diseases including neurodegenerative diseases, ischemic damage, autoimmune disorders, and several forms of cancer (2-6). Apoptosis was originally characterized by morphological features such as membrane blebbing, cell shrinkage, formation of apoptotic bodies, chromatin condensation, nucleolus loss, and chromatin fragmentation into single or multiple nucleosomes (7,8). In recent years, many molecules participating in the pathways mediating apoptosis have been identified (9). Caspase activation is a feature common to most of these pathways and leads to proteolytic cleavage of specific cell substrates (10-12), including poly(ADP-ribose) polymerase (PARP), lamins, histone H1 (13), and DNA protein kinase (14,15), as well as proteins involved in cell growth, survival, and death (11). Caspases also cleave the inhibitor of caspase-dependent DNase (ICAD), thus releasing active caspase-dependent DNase (CAD), which after translocation to the nucleus fragments chromatin (16). In addition, several reports have analyzed the fate of RNA during apoptosis. Indeed, [ 3 H]uridine pulse-chase experiments detected a twofold increase in RNA degradation rates in rat thymocytes after glucocorticoid treatment (17). More recently, cleavage of both 28S ribosomal RNA (rRNA) and Ro ribonucleoprotein-associated Y RNAs during apoptosis was shown (18, 19), but nothing is known regarding the fate of cytoplasmic mRNAs.In the immune system, apoptosis plays a key role both in the control of lymphocyte maturation ...

2′-AMP and 3′-AMP Inhibit Proliferation of Preglomerular Vascular Smooth Muscle Cells and Glomerular Mesangial Cells via A2B Receptors

“…Finally, in both PGVSMCs and GMCs, 2Ј,3Ј-cAMP has antiproliferative effects independent of 2Ј-AMP, 3Ј-AMP, and adenosine. Because mRNA turnover is a major endogenous source of 2Ј,3Ј-cAMP , increased mRNA metabolism stimulated by apoptosis (Del Prete et al, 2002) may inhibit PGVSMC and GMC growth and limit pathological remodeling in renal diseases via production of 2Ј,3Ј-cAMP, 2Ј-AMP, and 3Ј-AMP. Moreover, part of the pharmacology of rapamycin, which stimulates mRNA turnover (Banholzer et al, 1997;Hashemolhosseini et al, 1998;Albig and Decker, 2001), may be due to effects of 2Ј,3Ј-cAMP, 2Ј-AMP, and 3Ј-AMP.…”

Initiation factor modifications in the preapoptotic phase

“…For example, recent studies have identified significant degradation of some mRNA species at early times after treatment of cells with various inducers of apoptosis. 142,143 There is also cleavage of 28S rRNA in ribosomes in apoptotic cells, although this may be a somewhat later event. 144 In spite of these uncertainties, with our knowledge of the roles of individual initiation factors, it is possible to identify several specific effects that can be predicted from the changes induced by the phosphorylation and/or cleavage of these proteins during the early stages of the induction of cell death.…”

Rearrangement of nuclear ribonucleoprotein (RNP)‐containing structures during apoptosis and transcriptional arrest

“…Degradation of rRNA is, however, incomplete and it is likely that the same may occur with mRNA and tRNA. In fact, it has ben suggested by (Halicka et al 2000) that all nuclear RNAs do aggregate to rRNA in apoptotic nuclei; in addition, RNA molecules are extruded from the nucleus and remain in the cytoplasm of apoptotic cells in a sufficiently high amount to be detected by cytochemical techniques by fluorescence and electron microscopy (Biggiogera et al, 1998;Halicka et al, 2000).Del Prete et al (2002) have recently shown that cytoplasmic mRNA is degraded early during apoptosis, suggesting that the consequent block of protein synthesis could be a prerequisite for the cell to reach a point of no-return in the cell death program. Rutjes et al (1999) suggest that Y RNAs are nucleolytically degraded during apoptosis and the consequent block of Y RNA function could represent an early step of apoptotic cell death.…”

“…Del Prete et al (2002) have recently shown that cytoplasmic mRNA is degraded early during apoptosis, suggesting that the consequent block of protein synthesis could be a prerequisite for the cell to reach a point of no-return in the cell death program. Rutjes et al (1999) suggest that Y RNAs are nucleolytically degraded during apoptosis and the consequent block of Y RNA function could represent an early step of apoptotic cell death.…”