Houghton Lab

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Research Focus

The research interests of the laboratory of Janet Houghton focus on new target identification, development of novel small molecule inhibitors of critical targets, mechanisms of drug action, drug resistance, and translational therapeutics spanning basic research to clinical trials. Her lab researches the critical role of the transcription factor GLI in the survival of colon cancer cells and other cancers that constitutively express GLI and mutant KRAS genes. This involves determining mechanisms by which small molecule inhibitors of GLI induce extensive cell death by inhibiting GLI-dependent transcription and shutting off this signaling program. Mechanisms focus on the impact of GLI on transcriptional regulation, R-loop formation, and the initiation of DNA replication licensing in promoter regions. Her research over more than three decades has contributed significantly to our understanding of the mechanism of action of 5-fluorouracil and the role of leucovorin in colon cancer, how death receptor signaling regulated by members of the TNF receptor superfamily impacts cell death in cancers, and subsequently GLI as a therapeutic target for drug discovery in cancer.

Research Areas

Janet Houghton, Ph.D., has an extensive track record in cancer molecular and cell biology and therapeutics.  Her research areas include cell signaling, identification of new targets, regulation of GLI-dependent transcription and DNA licensing, regulation of GLI by oncogenic KRAS, death receptors of the TNF receptor superfamily, cancer molecular genetics in experimental models and human tumors, developmental therapeutics, mechanism of drug action, drug resistance, DNA damage signaling, transcription factors, cDNA microarray gene profiling for novel target identification, human solid tumors, colon carcinoma, and disease-specific phenotypes.

 

Current Research Focus

  • Constitutive GLI activation as a nodal point of convergence for oncogenic signaling pathways (HH-GLI, KRAS-GLI), and a critical therapeutic target in cancers
  • ŸMechanisms of GLI-dependent transcriptional inhibition, DNA damage, cell death
  • ŸThe role of GLI in DNA licensing
  • Drug discovery for small molecule GLI inhibitors with specific binding and mechanistic properties
  • Genetic mutations and mechanisms that determine constitutive GLI activation in colonic epithelial cell transformation
  • New targets in cancer therapeutics, drug resistance

 

Programs

In normal cellular processes the canonical Hedgehog (HH) signaling pathway is pivotal in embryonic development, tissue patterning, and differentiation.  The GLI genes (GLI1, GLI2) encode transcription factors that regulate target genes at the distal end of the HH pathway (SHH->PTCH->SMO->GLI). HH-GLI signaling is dysregulated in many types of human cancers with constitutive activation of GLI, advancing during progression and in metastatic disease. Oncogenic signaling pathways, including KRAS/BRAF in colon cancer, circumvent the HH-GLI axis to converge on and further activate GLI, which serves as a nodal channel for oncogenic signals.  GLI is constitutively activated early during colonic epithelial cell transformation, requiring interaction between mutant APC, KRAS and p53 signaling pathways.  The small molecule GLI inhibitor GANT61, which inhibits GLI-dependent transcription, induces extensive cell death in all human colon carcinoma cell line models examined in contrast to normal cells due to targeting constitutively activated GLI. GANT61 binds specifically to GLI and not to DNA or to other transcription factors, demonstrating selectivity and specificity for the GLI target, with no known off-target effects.  Mechanistically GANT61 inhibits the binding of GLI to the promoters of target genes with redistribution of key regulators of the transcriptional machinery (Pol II, DSIF, NELF, PTEFb) on chromatin.  GANT61 influences RNA:DNA hybrids formed within R-loop regions during transcriptional inhibition, and also inhibits DNA replication licensing in the promoters of GLI target genes. gH2AX foci are formed in S-phase and non-S-phase cells following inhibition of transcription and DNA licensing, accumulating at the G1/S boundary where DNA damage is recognized at the initiation of DNA replication.  Cells accumulate in at the initiation of S-phase. DNA replication forks can stall, inhibiting initiation of DNA replication from unfired origins at early replicons. This further inhibits progression through S-phase, and cells undergo apoptosis. Alternatively, critical regulators of the G1/S boundary, that are GLI targets, are downregulated following GANT61 treatment, including FOXM1, CDC6 and CDT1.  FOXM1 is a transcription factor that plays a key role in the G1/S transition, is transcriptionally regulated by GLI1, and is an effector of KRAS/BRAF signaling.  CDC6 is involved in assembly of the PreReplication Complex (PRC), initiation of DNA replication, early S-phase progression, and activation of the intra-S-phase checkpoint.  Inhibition of the GLI-regulated FOXM1/CDC6 pathway and the G1/S transition by GANT61 may prevent progression from early S-phase.  Alternatively, we have determined that the DNA licensing factor CDT1 is a transcriptional target of GLI, downregulated following treatment with GANT61, and may also determine stalled progression from early S.

 

Current projects

Mechanism of inhibition of GLI-dependent transcription by GANT61

Role of R-loops (RNA:DNA hybrids, ssDNA) in the mechanism of DNA damage and early S-phasearrest

Role of DNA replication licensing in the mechanism of DNA damage and early S-phase arrest

Role of the FOXM1/CDC6 and GLI1/CDT1 pathways in inhibition of the G1/S transition

Drug discovery initiatives for inhibitors of GLI and oncogenic KRAS-dependent GLI activation

Mechanism(s) of induction of constitutive GLI activation during colonic epithelial cell transformation.

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Janet Houghton, Ph.D.

Distinguished Fellow and Emil Hess Endowed Chair, Cancer Biology

Janet Houghton is a Distinguished Fellow and Emil Hess Endowed Chair in Cancer Biology in the Oncology Department. She leads research in drug discovery and mechanism-based studies, determining the critical role of the transcription factor GLI in survival of colon cancer cells and other cancers that constitutively express GLI and mutant KRas genes. Her education and training were in the United Kingdom with the Ph.D. conferred from the University of London. She moved to the United States, where she developed an independent career at St. Jude Children’s Research Hospital in Memphis, Tennessee, later moving to the Cleveland Clinic to focus on adult colorectal cancer, and subsequently joining Southern Research. Her research has resulted in the publication of 146 original peer-reviewed publications and 10 book chapters. She serves on several NIH Study Sections and Advisory Boards and has been Senior Editor for the international journal, Cancer Research, for over 12 years.

[ Read Full Bio Here ]

Lab Members

Ruowen Zhang, Ph.D

Postdoctoral Research Fellow

Ruowen Zhang earned his M.D. in Forensic Medicine at West China Medical Center of Sichuan University, China in 2007. He then earned his Ph.D. in Biochemistry at Queen’s University of Belfast, UK in December 2011. While a Doctoral student, he identified twelve novel bioactive peptides from frog and toad skin samples by molecular biology technology, and optimized protocols for protein expression in bacterium using the pET system. He next joined Shenyang Sunshine Pharmaceutical Co., LTD, China, as a R&D Sceintist between 2011 and 2012. He next spent one year as a Visiting Scholar at Nelson Institute of Environmental Medicine, at New York University School of Medicine until October 2013. After which, he spent another year as a visiting scholar in the Department of Pathology at the University of North Dakota. In December of 2014, he joined the University of Alabama at Birmingham as a post-doctoral researcher to study the mechanism of cell reprogramming, investigate epigenetic regulation to maintain pluripotency and self-renewal in human pluripotent stem cells, seek out enhancers or barriers which regulate iPSC generation, and investigate the function of cell cycle in the reprogramming process. In 2016, Ruowen Zhang was recruited to Southern Research, where he is currently working in the lab of Dr. Janet Houghton. Ruowen’s main research focus is to discover novel anti-cancer drugs, especially against colorectal cancer, and perform research on underlying mechanisms of Gli-inhibitor induced DNA damage.

Publications

Houghton Publications:

PubMed

Research Gate

Zhang Publications:

PubMed

Relevant Links

National Cancer Institute: www.cancer.gov

American Cancer Society: www.cancer.org

DEPARTMENT OF DEFENSE – CONGRESSIONALLY DIRECTED MEDICAL RESEARCH PROGRAMS: http://cdmrp.army.mil/

UAB Comprehensive Cancer Center: http://www3.ccc.uab.edu/

 



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