Autoregulatory control of beta-tubulin mRNA stability is linked to translation elongation.

Abstract

Tubulin synthesis in animal cells is controlled in part by an autoregulatory mechanism that modulates the stability of ribosome-bound tubulin mRNAs. For f3 tubulin, the initial recognition event for this selective RNA instability has previously been shown to be a cotranslational binding (presumably by tubulin itself) to the nascent amino-terminal 13-tubulin tetrapeptide just after it emerges from the ribosome. Although this "autoregulation" of tubulin expression is thus obligatorily linked to the translation process, the mechanism of how a cotranslational protein-protein binding event ultimately triggers RNA degradation is unknown. Using protein synthesis inhibitors to slow and ultimately to block translation elongation, we now show that the mRNA destabilization pathway requires ongoing ribosome translocation.In most animal cells, the appropriate quantitative level of tubulin expression is established in part through an autoregulatory pathway in which the apparent intracellular concentration of tubulin heterodimers (comprising one a-and one P-tubulin polypeptide) modulates the stability of tubulin mRNAs (1-7). Evidence for such a self-regulated pathway emerged initially from experiments with inhibitors that induced microtubule depolymerization: the corresponding rise in the intracellular concentration of unassembled subunits leads to a rapid and specific depression of synthesis of both a-and f3-tubulin polypeptides. This decrease in synthesis [induced either by treatment with microtubule-destabilizing drugs or by direct microinjection of tubulin subunits (8)] was next shown to be the result of a posttranscriptional mechanism that alters the stability of cytoplasmic tubulin mRNAs after changes in the concentration of unpolymerized tubulin subunits (3-5, 9). The sequences that are necessary and sufficient to specify f3-tubulin mRNAs as substrates for this autoregulated instability have been shown by DNA transfection experiments (6) to lie within the first 13 translated nucleotides [which encode the first four ,3-tubulin amino acids (Met-Arg-Glu-Ile)]. Further, by using inhibitors of protein synthesis and transfection ofgenes bearing premature translation termination codons, it was determined that only tubulin mRNAs that are attached to polyribosomes are destabilized by increased subunit concentrations (6, 10). Most recently, introduction of 25 different nucleotide base substitutions into this 13-base regulatory element has documented that 13-tubulin RNAs are selectively targeted as substrates for destabilization not through recognition of specific RNA sequences but rather through cotranslational recognition of the amino-terminal P-tubulin tetrapeptide after its emergence from the ribosome (7).Many important details of this mRNA instability pathway remain to be determined. For example, it is not known how the putative interaction involving the nascent tubulin polypeptide and a cellular factor(s) (presumably the tubulin heterodimer) can be transduced through the ribosome to yield enhanced degradation of the ...

Regulation of T-cell antigen receptor (TCR) alpha-chain expression by TCR beta-chain transcripts.

“…V, transcripts may also function indirectly through an unidentified mediator. The absence of a 13-chain transcript could conceivably render the a-chain transcript susceptible to degradation by a sequence-specific RNase or any RNase associated with a common cellular structure such as the ribosome (24). However, transiently transfected TCR a-chain cDNA (in the same expression vector, pBJ-neo) was expressed at similar levels in the wild-type and mutant cells (data not shown).…”

A small segment of the MAT alpha 1 transcript promotes mRNA decay in Saccharomyces cerevisiae: a stimulatory role for rare codons.

“…Moreover, nonuniform translation rates along individual mRNAs have been implicated as being important in a number of cellular processes, including protein secretion, frameshifting, transcriptional attenuation, and protein folding (2,4,11,39,43). Indeed, it has been postulated that ribosomal pausing may be involved in the decay of other mRNAs (6,13).…”

Fungal Elicitor-Induced Bean Proline-Rich Protein mRNA Down-Regulation Is Due to Destabilization That Is Transcription and Translation Dependent.

“…The P-tubulin mRNA half-life in etiolated oat leaves was shown to be about 1.5 hr (Byrne et al, 1993). In a numberof mammalian cell cultures, a-tubulin and P-tubulin mRNA half-lives are 1 to 2 hr, and these mRNAs are destabilized by high levels of tubulin heterodimers (Cleveland et al, 1981;Pachter et ai., 1987;Gay et al, 1989). It is unknown whether funga1 elicitor treatment of plant cells triggers P-tubulin mRNA decay by a similar mechanism.…”