Enhanced Stability of Urokinase‐Type Plasminogen Activator mRNA in Metastatic Breast Cancer MDA‐MB‐231 Cells and LLC‐PK₁ Cells Down‐Regulated for Protein Kinase C — Correlation with Cytoplasmic Heterogeneous Nuclear Ribonucleoprotein C

Abstract

In LLC-PK, cells, urokinase-type plasminogen activator (uPA) mRNA has a short half-life of 70 min. We have previously demonstrated that most of the regulatory regions responsible for the rapid turnover of uPA mRNA in LLC-PK, cells reside in its 3' untranslated region (3' UTR), where there are at least three regulatory sites, one of which is A+U-rich. This A+U-rich sequence mediates uPA mRNA stabilization induced by protein kinase C (PKC) down-regulation. In this work, we found that uPA mRNA is rather stable in MDA-MB-231 cells with a half-life of 17 h. We compared the stability of hybrid globin mRNA containing different parts of uPA mRNA in its 3' UTR and found that the A+U-rich sequence of uPA mRNA renders otherwise stable globin mRNA unstable in LLC-PK, cells but not in MDA-MB-231 cells. We identified a cytoplasmic protein of 40 kDa (p40) which specifically interacts with the A+U-rich sequence. Levels of p40 activity as detected by ultraviolet cross-linking were higher in MDA-MB-231 and PKC-down-regulated LLC-PK, cells than in untreated LLC-PK, cells. Prior treatment of the cytoplasm with a specific antibody against heterogeneous nuclear ribonucleoprotein C (hnRNP C) significantly reduced p40 activity. These results suggest a correlation between the A+U-rich sequence-dependent uPA mRNA stabilization in vivo and the binding of hnRNP C to the A+U-rich sequence in vitro.

Urokinase Plasminogen Activator/Urokinase-specific Surface Receptor Expression and Matrix Invasion by Breast Cancer Cells Requires Constitutive p38α Mitogen-activated Protein Kinase Activity

“…Cross-linking ␣ L ␤ 2 integrin in T lymphocytes was also found to promote uPAR mRNA stability and uPAR expression (24). Furthermore, both studies indicated that uPA and uPAR mRNA stability is controlled through the AU-rich sequences in 3Ј-UTR of uPA and uPAR mRNA (24,45). In our studies, we found that p38 MAPK activity had little effect on uPA and uPAR promoter activities (Fig.…”

“…PMA was found to transcriptionally up-regulate uPAR expression dependent on AP-1 site in uPAR promoter region (16). In terms of mRNA stability, previous studies reported that the half-life of uPA mRNA in pig epithelial LLC-PK1 cells was 70 min, whereas in contrast its half-life in breast cancer MDA-MB-231 cells is 17 h, suggesting that uPA expression can be regulated at the level of mRNA stability (45). Cross-linking ␣ L ␤ 2 integrin in T lymphocytes was also found to promote uPAR mRNA stability and uPAR expression (24).…”

Differentiation-Induced Internal Translation of c-sis mRNA: Analysis of the cis Elements and Their Differentiation-Linked Binding to the hnRNP C Protein

“…Nevertheless, a growing number of studies show the cytoplasmic interaction of hnRNP C proteins with AU-rich sequences of certain labile mRNAs (17,35,37,57,60). Interestingly, cytoplasmic localization of hnRNP C RNA binding activity was correlated with TPA treatment of peripheral blood mononuclear cells (46) and of LLC-PK 1 cells (37). We show here that following TPA-induced differentiation of K562 cells, most of the hnRNP C protein remained nuclear (Fig.…”

“…However, the short fragment 14, containing the predicted structure Y F as a single Y-shaped motif, had a basal IRES value of 41%. Fragments containing the predicted Y D as the single Y motif (fragments 9 through 13) were also active as IRESs (31,34,37,26, and 26%, respectively). The low IRES values of these fragments, which are spread throughout the complete 5Ј UTR, may reflect the stability of the Y D structure within each fragment, the importance of the Y D context among Based on the updated sequence, a conserved structure of the c-sis 5Ј UTR was predicted by a combination of phylogenetic, thermodynamic, and statistical methods as described previously (4).…”

“…The C proteins, known as ultimate nuclear proteins, were shown to contain a nuclear localization signal as well as a nuclear retention sequence (NRS) (10,36). Nevertheless, a growing number of studies show the cytoplasmic interaction of hnRNP C proteins with AU-rich sequences of certain labile mRNAs (17,35,37,57,60). Interestingly, cytoplasmic localization of hnRNP C RNA binding activity was correlated with TPA treatment of peripheral blood mononuclear cells (46) and of LLC-PK 1 cells (37).…”