LIMK2 is a serine/threonine/tyrosine kinase that promotes tumor cell invasion and metastasis by phosphorylating cell proteins and altering their functions. There is a need to find tumor-specific substrates for LIMK2 in order to understand the downstream pathway of these substrates, their function, and how they are regulated by LIMK2. Recently, our labrotory identified LIMK2 as an excellent target for curing castration-resistant prostate cancer (CRPC). In this study, we identify two novel substrates for LIMK2 in CRPC: speckle-type POZ protein (SPOP), and Y-box binding protein-1 (YBX1). While LIMK2 negatively regulates SPOP, it positively regulates YBX1 − both by phosphorylation using in-vitro kinase assays. A study in our labrotory also proved that LIMK2 regulates Aurora A kinase (AURKA), where AURKA directly phosphorylates LIMK2. AURKA is a serine/threonine kinase that regulates cell cycle during mitosis; it is known to be upregulated, with uncontrolled activity, in many types of cancer, including prostate cancer. It is therefore important to identify new substrates for AURKA, especially in light of reported lethality in early embryonic mice, in association with AURKA-knockout. In other words, targeting AURKA directly may cause severe toxicity, a finding that has prevented direct inhibitors from passing Phase II clinical trials. In this study, we also identified SPOP and YBX1 as direct substrates for AURKA. Our results confirm what we know about the LIMK2/AURKA relationship: that AURKA negatively regulates SPOP and positively regulates YBX1. Targeting LIMK2 and AURKA indirectly through SPOP, YBX1 and its other substrates holds tremendous therapeutic potential in treating prostate cancer. With this, we open the door for researches to investigate the direct phosphorylation of SPOP and YBX1 in other types of cancer cells known to have overexpression in SPOP and/or YBX1.

Despite recent advances in antiretroviral therapy, nearly 37 million people continue to live with human immunodeficiency virus (HIV). Basic and applied research on the assembly of HIV could be enhanced by using a genetically tractable organism, such as yeast, rather than mammalian cells. While previous studies showed that expression of the HIV Gag polyprotein in Saccharomyces cerevisiae spheroplasts resulted in the production of virus-like particles (VLPs), many questions regarding the utility of yeast in HIV assembly remain uninvestigated. Here, we report use of S. cerevisiae for both the production of VLPs with selectively packaged RNA and to evaluate the human Y-box-binding protein 1 (YB-1) in selective RNA packaging into VLPs. Our data reveal: (1) When co-expressed alongside HIV-1 Gag, an RNA mammalian expression cassette is selectively encapsidated and released in VLPs produced from spheroplasts; (2) Inclusion of the 5’UTR-5’Gag RNA upstream of the mammalian expression cassette greatly increased the selectivity to which non-viral RNA was packaged into VLPs; and (3) heterologous expression of the human YB-1 protein in S. cerevisiae did not facilitate the selective packaging of viral RNA into VLPs, likely due to inability to bind upstream elements in the HIV-1 viral RNA. Overall, this research provides a key first step in the use of yeast for the production of viral vectors used in gene therapy, and lays a foundation for further experiments investigating the role of YB-1 and other host proteins in selective RNA packaging.