Begoña Ballester-Lurbe

Rnd3 is an atypical member of the Rho GTPase family whose activity is mainly regulated by expression, localization and protein stability rather than canonical GDP/GTP cycling. In cancer, Rnd3 has been described both as a tumor suppressor and as a tumor-promoting factor, creating an apparent functional paradox. We propose that this paradox is resolved by a mechanistic invariant: Rnd3 exerts a conserved inhibition of RhoA/ROCK1-dependent actomyosin contractility, whose phenotypic output is redirected by context-specific accessory effectors rather than reversed. In this review, we revisit this paradox by integrating evidence from mechanistic studies, tumor models and patient-associated datasets. We propose that Rnd3 should not be interpreted through a binary oncogene/tumor-suppressor framework, but rather as a context-dependent regulator of tumor cell state. In many tumor settings, Rnd3 repression or loss of Rnd3 function favors proliferation, apoptosis resistance and therapy resistance through pathways involving Notch, NF-κB, EGFR/ERK, EZH2-dependent chromatin regulation, m6A-mediated RNA control, microRNAs and chaperone-mediated autophagy. However, in selected contexts, including RTK-driven glioblastoma, hepatocellular carcinoma, non-small-cell lung cancer, melanoma and gastric cancer, Rnd3 may support tumor fitness, migration or invasive plasticity. We therefore propose a functional stratification model in which Rnd3 output depends on the biological process, tumor lineage, pathway activity and mechanical state of the cell.

Background: Multiple myeloma (MM) is the second most common hematologic neoplasm which is characterized by proliferation and infiltration of plasmatic cells in the bone marrow. Currently, MM is considered incurable due to resistance to treatment. The CRISPR/Cas9 system has emerged as a powerful tool for understanding the role of different genetic alterations in the pathogenesis of hematologic malignancies in both cell lines and mouse models. Despite current advances of gene editing tools, the use of CRISPR/Cas9 technology for gene editing of MM have not so far been extended. In this work, we want to repress Rnd3 expression, an atypical Rho GTPase involved in several cellular processes, in MM cell lines using a CRISPR interference strategy. Results: We have designed different guide RNAs and cloning them into a lentiviral plasmid, which contains all the machinery necessary for developing the CRISPR interference strategy. We co-transfected the HEK 293T cells with this lentiviral plasmid and 3rd generation lentiviral envelope and packaging plasmids to produce lentiviral particles. The lentiviral particles were used to transduce two different multiple myeloma cell lines, RPMI 8226 and JJN3, and downregulate Rnd3 expression. Additionally, the impact of Rnd3 expression absence was analyzed by a transcriptomic analysis consisting of 3’ UTR RNA sequencing. The Rnd3 knock-down cells showed a different transcriptomic profile in comparison to control cells. Conclusions: We have developed a CRISPR interference strategy to generate stable Rnd3 knockdown MM cell lines by lentiviral transduction. We have evaluated this strategy in two MM cell lines, and we have demonstrated that Rnd3 silencing works both at transcriptional and protein level. Therefore, we propose CRISPR interference strategy as an alternative tool to silence gene expression in MM cell lines. Furthermore, Rnd3 silencing produces changes in the cellular transcriptomic profile.