MILIP Binding to tRNAs Promotes Protein Synthesis to Drive Triple-Negative Breast Cancer.

Patients with triple-negative breast cancer (TNBC) have a poor prognosis due to the lack of effective molecular targets for therapeutic intervention. Here we found that the long noncoding RNA (lncRNA) MILIP supports TNBC cell survival, proliferation, and tumorigenicity by complexing with transfer RNAs (tRNA) to promote protein production, thus representing a potential therapeutic target in TNBC. MILIP was expressed at high levels in TNBC cells that commonly harbor loss-of-function mutations of the tumor suppressor p53, and MILIP silencing suppressed TNBC cell viability and xenograft growth, indicating that MILIP functions distinctively in TNBC beyond its established role in repressing p53 in other types of cancers. Mechanistic investigations revealed that MILIP interacted with eukaryotic translation elongation factor 1 alpha 1 (eEF1α1) and formed an RNA-RNA duplex with the type II tRNAs tRNALeu and tRNASer through their variable loops, which facilitated the binding of eEF1α1 to these tRNAs. Disrupting the interaction between MILIP and eEF1α1 or tRNAs diminished protein synthesis and cell viability. Targeting MILIP inhibited TNBC growth and cooperated with the clinically available protein synthesis inhibitor omacetaxine mepesuccinate in vivo. Collectively, these results identify MILIP as an RNA translation elongation factor that promotes protein production in TNBC cells and reveal the therapeutic potential of targeting MILIP, alone and in combination with other types of protein synthesis inhibitors, for TNBC treatment. SIGNIFICANCE: LncRNA MILIP plays a key role in supporting protein production in TNBC by forming complexes with tRNAs and eEF1α1, which confers sensitivity to combined MILIP targeting and protein synthesis inhibitors.

High nerve density in breast cancer is associated with poor patient outcome.

Active crosstalk between the nervous system and breast cancer cells has been experimentally demonstrated in vitro and in animal models. However, low frequencies of peripheral nerve presence in human breast cancers reported in previous studies (~30% of cases) potentially negate a major role of the nervous system in breast cancer development and progression. This study aimed to clarify the incidence of nerves within human breast cancers and to delineate associations with clinicopathological features. Immunohistochemical staining was conducted in formalin-fixed paraffin-embedded breast cancer tissue sections using antibodies against the pan-neuronal markers protein gene product 9.5 and growth-associated protein 43, and the sympathetic nerve-specific marker tyrosine hydroxylase. Nerve trunks and isolated nerve fibers were quantitated. The chi-squared test was used to determine the associations between nerve counts and clinicopathological parameters. The log-rank test was used to compare differences in patient progression-free survival (PFS) and overall survival (OS). The overall frequency of peripheral nerves in breast cancers was 85%, a markedly higher proportion than reported previously. Of note, most nerves present in breast cancers were of the sympathetic origin. While high density of nerve trunks or isolated nerve fibers was associated with poor PFS and OS of patients, high nerve trunk density appeared also to predict poor patient PFS independently of lymph node metastasis. Innervation of breast cancers is a common event correlated with poor patient outcomes. These findings support the notion that the nervous system plays an active role in breast cancer pathogenesis.

Anti-estrogenic mechanism of unliganded progesterone receptor isoform B in breast cancer cells.

Over half of breast cancer cases are estrogen-dependent and strategies to combat estrogen-dependent breast cancer have been to either block the activation of estrogen receptor (ER) or diminish the supply of estrogens. Our previous work documented that estrogen-independent expression of progesterone receptor (PR) in MCF-7 cells markedly disrupted the effects of estrogen. In this study, we have developed an adenovirus-mediated gene delivery system to study the specific involvement of PR isoform A (PR-A) and PR-B in the anti-estrogenic effect and its mechanism of action. The results revealed that PR-B, but not PR-A, exhibited distinct anti-estrogenic effect on E2-induced cell growth, gene expression, and ER-ERE interaction in a ligand-independent manner. The anti-estrogenic effect of PR-B was also associated with heightened metabolism and increased cellular uptake of estradiol-17 beta (E2). We have also found that the B-upstream segment of PR-B alone was able to inhibit E2-induced ER-ERE interaction and cellular uptake of E2. Although PR-A alone did not affect E2-induced ER activity, it antagonized the anti-estrogenic effect of PR-B in a concentration-dependent manner. The findings suggest an important mechanism of maintaining a favorable level of ER activity by PR-A and PR-B in estrogen target cells for optimal growth and differentiation. The potential anti-estrogenic mechanism of PR-B may be exploited for breast cancer therapy.