Doctoral Student, University of Cape Town/ Health Sciences Faculty


Nuclear import protein KpnB1 as an anti-cancer target

Cancer is a major human disaster and statistics have shown that it kills more people yearly than HIV, tuberculosis and malaria combined. The new cancer cases are being discovered and mortality rate is constantly on the increase and this is in spite of recent advances in oncology. Most cancers are discovered at late and mostly untreatable stages. This necessitates the need to identify new markers of cancers and then begin treatment as soon as possible. Furthermore, conventional chemotherapy has not shown much success as most patients have shown terrible side effects. There is a need to focus on targeted therapy which identifies the particular addiction of cancer cells and uses that to destroy them.

Various studies have found Karyopherin Beta 1 (KpnB1) to be involved in driving the process of carcinogenesis when it is expressed beyond the normal threshold. Elevated expression of KpnB1 has been found in cancers such as ovarian, cervical, oesophageal and gastric cancers among many others. KpnB1 is a protein that is involved in the transport of numerous protein which are usually involved in cell growth and division from the cytoplasm into the nucleus so they can carry out their primary functions. The importance of this protein in many cell processes indicates why its deregulation is oncogenic.

There are no commercially available drugs targeting KpnB1 for treatment in cancer patients. In silico screening was done by researchers in our Laboratory to identify potential drug that can bind to and inhibit KpnB1 function. Our team is currently describing three potential inhibitors of KpnB1 function in vitro using cervical, oesophageal and ovarian cancers as model as well as in vivo using mouse xenograft models. The three inhibitors have shown significant anti-cancer properties in vivo and in vitro. Furthermore, these inhibitors have had little or no effects on non-cancer cells both in vitro and in vivo.

We aim that these small molecule inhibitors of KpnB1 may generate anti-cancer treatment for cancers of different tissue origin in cancer patients which will be more effective and less toxic in comparison to conventional chemotherapy.


Structural Biology and Regulation of Protein Import into the Nucleus

Abstract: Proteins are translated in the cytoplasm, but many need to access the nucleus to perform their functions. Understanding how these nuclear proteins are transported through the nuclear envelope and how the import processes are regulated is therefore an important aspect of understanding cell function. Structural biology has played a key role in understanding the molecular events during the transport processes and their regulation, including the recognition of nuclear targeting signals by the corresponding receptors. Here, we review the structural basis of the principal nuclear import pathways and the molecular basis of their regulation. The pathways involve transport factors that are members of the β-karyopherin family, which can bind cargo directly (e.g., importin-β, transportin-1, transportin-3, importin-13) or through adaptor proteins (e.g., importin-α, snurportin-1, symportin-1), as well as unrelated transport factors such as Hikeshi, involved in the transport of heat-shock proteins, and NTF2, involved in the transport of RanGDP. Solenoid proteins feature prominently in these pathways. Nuclear transport factors recognize nuclear targeting signals on the cargo proteins, including the classical nuclear localization signals, recognized by the adaptor importin-α, and the PY nuclear localization signals, recognized by transportin-1. Post-translational modifications, particularly phosphorylation, constitute key regulatory mechanisms operating in these pathways.

Pub.: 30 Oct '15, Pinned: 28 Jul '17

Targeting the Nuclear Import Receptor Kpnβ1 as an Anticancer Therapeutic.

Abstract: Karyopherin beta 1 (Kpnβ1) is a nuclear transport receptor that imports cargoes into the nucleus. Recently, elevated Kpnβ1 expression was found in certain cancers and Kpnβ1 silencing with siRNA was shown to induce cancer cell death. This study aimed to identify novel small molecule inhibitors of Kpnβ1, and determine their anticancer activity. Anin silicoscreen identified molecules that potentially bind Kpnβ1 and Inhibitor of Nuclear Import-43, INI-43 (3-(1H-benzimidazol-2-yl)-1-(3-dimethylaminopropyl)pyrrolo[5,4-b]quinoxalin-2-amine) was investigated further as it interfered with the nuclear localization of Kpnβ1 and known Kpnβ1 cargoes NFAT, NFκB, AP-1, and NFY and inhibited the proliferation of cancer cells of different tissue origins. Minimum effect on the proliferation of noncancer cells was observed at the concentration of INI-43 that showed a significant cytotoxic effect on various cervical and esophageal cancer cell lines. A rescue experiment confirmed that INI-43 exerted its cell killing effects, in part, by targeting Kpnβ1. INI-43 treatment elicited a G2-M cell-cycle arrest in cancer cells and induced the intrinsic apoptotic pathway. Intraperitoneal administration of INI-43 significantly inhibited the growth of subcutaneously xenografted esophageal and cervical tumor cells. We propose that Kpnβ1 inhibitors could have therapeutic potential for the treatment of cancer.Mol Cancer Ther; 15(4); 1-14. ©2016 AACR.

Pub.: 03 Feb '16, Pinned: 28 Jul '17

The effect of nanoparticle size and NLS density on nuclear targeting in cancer and normal cells; impaired nuclear import and aberrant nanoparticle intracellular trafficking in glioma.

Abstract: The cell nucleus is an interesting target in many diseases with particular interest in cancer. Previously, nuclear targeted small and large chitosan nanoparticles (S-NPs≈25nm, and L-NPs≈150nm respectively), modified with low, intermediate and high densities of NLS (L-NLS, I-NLS and H-NLS) were developed and assessed in L929 fibroblasts. However, to evade apoptosis and stimulate tumor growth cancer cells are capable of manipulating the nuclear-cytoplasmic transport on many levels, making NPs that are capable of nuclear targeting in normal cells incapable of doing so in cancer. For such reason, here, the nuclear delivery efficiency of S-NPs and L-NPs was assessed as a function of their NLS density in cancer and non-cancer cells. For S-NPs, in all cells tested, NLS was unnecessary for nuclear delivery; unmodified S-NPs showed higher nuclear delivery than NLS-S-NPs due to their ability to gain nuclear entry in a passive manner. For L-NPs, L-NLS-L-NPs showed ≈ 8.5, 33, 1.8 and 7.2 fold higher nuclear deliveries than H-NLS-L-NPs in L929 fibroblasts, primary human fibroblasts, HEK 293 and lung cancer cells, respectively. In glioma however, unmodified L-NPs showed highest nuclear delivery, whereas NLS-L-NPs were retained in the cytoplasm. Experiments conducted in the presence of inhibitors of the classical nuclear import pathway indicated that due to overexpression of importin α, classical nuclear import in glioma is impaired leading to aberrant NP intracellular trafficking and nuclear import.

Pub.: 04 Mar '17, Pinned: 28 Jul '17

Nuclear Import of JAK1 is Mediated by a Classical NLS and is Required for Survival of Diffuse Large B-cell Lymphoma.

Abstract: Janus kinases (JAKs) are non-receptor tyrosine kinases that are generally found in association with cytokine receptors. In the canonical pathway, roles of JAKs have well been established in activating signal transducers and activators of transcription (STATs) in response to cytokine stimulation to modulate gene transcription. In contrast, a non-canonical role of JAK2 has recently been discovered in which JAK2 in the nucleus imparts the epigenetic regulation of gene transcription through phosphorylation of tyrosine 41 on the histone protein H3. Recent work further demonstrated that this non-canonical mechanism is conserved with JAK1, which is activated by the autocrine cytokines IL-6 and IL-10 in activated B-cell-like diffuse large B cell lymphoma (ABC DLBCL), a cancer type that is particularly difficult to treat and has poor prognosis. However, how JAK1 gains access to the nucleus to enable epigenetic regulation remains undefined. Here we investigated this question and revealed that JAK1 has a classical nuclear localization signal (cNLS) toward the N-terminal region, which can be recognized by multiple importin alpha isoforms. Moreover, the nuclear import of JAK1 is independent of its kinase activity but is required for the optimal expansion of ABC DLBCL cells in vitro.This study demonstrates that the nuclear import of JAK1 is essential for the optimal fitness of ABC DLBCL cells and targeting JAK1 nuclear localization is a potential therapeutic strategy for ABC DLBCL.

Pub.: 30 Dec '16, Pinned: 28 Jul '17

KPNB1-mediated nuclear import is required for motility and inflammatory transcription factor activity in cervical cancer cells.

Abstract: Karyopherin β1 is a nuclear import protein involved in the transport of proteins containing a nuclear localisation sequence. Elevated Karyopherin β1 expression has been reported in cancer and transformed cells and is essential for cancer cell proliferation and survival. Transcription factors such as NFĸB and AP-1 contain a nuclear localisation sequence and initiate the expression of multiple factors associated with inflammation and cancer cell biology. Our study investigated the effect of inhibiting nuclear import via Karyopherin β1 on cancer cell motility and inflammatory signaling using siRNA and the novel small molecule, Inhibitor of Nuclear Import-43, INI-43. Inhibition of Karyopherin β1 led to reduced migration and invasion of cervical cancer cells. Karyopherin β1 is essential for the translocation of NFĸB into the nucleus as nuclear import inhibition caused its cytoplasmic retention and decreased transcriptional activity. A similar decrease was seen in AP-1 transcriptional activity upon Karyopherin β1 inhibition. Consequently reduced interleukin-6, interleukin-1 beta, tumour necrosis factor alpha and granulocyte macrophage colony stimulating factor expression, target genes of NFkB and AP-1, was observed. Migration studies inhibiting individual transcription factors suggested that INI-43 may affect a combination of signaling events. Our study provides further evidence that inhibiting KPNB1 has anti-cancer effects and shows promise as a chemotherapeutic target.

Pub.: 22 Apr '17, Pinned: 28 Jul '17