Biology subjects

Stephan, C.

Publications and source records attributed to Stephan, C..

5 recordsLinked to original sources

bioRxiv2025

Discovery of Small Molecules and a Druggable Groove That Regulate DNA Binding and Release of the AP1 Transcription Factor DeltaFOSB

{Delta}FOSB, a member of the AP1 family of transcription factors, mediates long-term neuroadaptations underlying drug addiction, seizure-related cognitive decline, dyskinesias, and several other chronic conditions. AP1 transcription factors are notoriously difficult to modulate pharmacologically due to the absence of well-defined binding pockets. Here, we identify a novel site on {Delta}FOSB, located outside the DNA-binding cleft, that accommodates small molecules. We show that sulfonic acid-containing compounds bind to this site via an induced-fit mechanism, reorienting side chains critical for DNA binding, and that they may hinder the {Delta}FOSB bZIP -helix from binding to the major groove of DNA. In vivo, direct administration of one such compound, JPC0661, into the brain reduces {Delta}FOSB occupancy at genomic AP1 consensus sites by approximately 60% as determined by CUT&RUN-sequencing. These findings suggest that DNA binding and release by AP1 transcription factors can be controlled via small molecules that dock into a novel site that falls outside of the DNA-binding cleft. Minimal sequence conservation across 29 bZIP domain-containing transcription factors in this druggable groove suggests that it can be exploited to develop AP1-subunit-selective compounds. Our studies thus reveal a novel strategy to design small-molecule inhibitors of {Delta}FOSB and other members of the bZIP transcription factor family.

neuroscience↗

bioRxiv2024

Structural basis of dual BACH1 regulation by SCFFBXO22 and SCFFBXL17

BTB and CNC homolog 1 (BACH1) is a master transcriptional regulator of the cellular oxidative stress response and pro-metastatic oncogene. Post-translational stability of BACH1 is tightly regulated by distinct F-box ubiquitin ligases, including SCFFBXO22 and SCFFBXL17. However, the molecular details have been elusive. Here, we reveal a structural switch in FBXO22 that controls the recognition of a three-dimensional degron in the BACH1 BTB domain, thus explaining its specificity for dimeric BACH1. We describe how cancer-associated mutations in FBXO22 modulate binding and ubiquitylation of BACH1. Further, we reveal that cancer-related mutations or cysteine-modifications destabilize the BTB domain and redirect BACH1 to FBXL17, where it is recognized as a monomer. This explains how complementary ligases post-translationally regulate BACH1 depending on the state of its BTB domain. Our findings provide mechanistic insights into the regulation of the oxidative stress response and may spur therapeutic strategies to targeting oxidative stress-related disorders and metastatic cancers.

biophysics↗

bioRxiv2021

Tibial nerve stimulation increases vaginal blood perfusion and bone mineral density and yield load in ovariectomized rats

Introduction and HypothesisHuman menopause transition and post-menopausal syndrome, driven by reduced ovarian activity and estrogen levels, are associated with an increased risk for symptoms including but not limited to sexual dysfunction, metabolic disease, and osteoporosis. Current treatments are limited in efficacy and may have adverse consequences, so investigation for additional treatment options is necessary. Previous studies have demonstrated that tibial nerve stimulation (TNS) or electro-acupuncture near the tibial nerve are minimally invasive treatments that increase vaginal blood perfusion or serum estrogen in the rat model. We hypothesized that TNS would protect against harmful reproductive and systemic changes associated with menopause. MethodsWe examined the effects of twice weekly TNS (0.2 ms pulse width, 20 Hz, 2x motor threshold) under ketamine-xylazine anesthesia in ovariectomized (OVX) female Sprague Dawley rats on menopause-associated physiological parameters including serum estradiol, body weight, blood glucose, bone health, and vaginal blood flow. Rats were split into three groups (n = 10 per group): 1) intact control (no stimulation), 2) OVX control (no stimulation), and 3) OVX stimulation (treatment group). ResultsTNS did not affect serum estradiol levels, body weight, or blood glucose. TNS transiently increased vaginal blood perfusion during stimulation for up to 5 weeks after OVX and increased areal bone mineral density and yield load of the right femur (side of stimulation) compared to the unstimulated OVX control. ConclusionTNS may ameliorate some symptoms associated with menopause. Additional studies to elucidate the full potential of TNS on menopause-associated symptoms under different experimental conditions are warranted. SummaryPercutaneous tibial nerve stimulation increases vaginal blood perfusion, areal bone mineral density, and femur yield load in an ovariectomized rat model of menopause.

physiology↗

bioRxiv2019

Ultra-compliant carbon nanotube stretchable direct bladder interface

The bladder, stomach, intestines, heart, and lungs all move dynamically to achieve their purpose. A long-term implantable device that can attach onto an organ, sense its movement, and deliver current to modify the organ function would be useful in many therapeutic applications. The bladder, for example, is a smooth muscle organ that can suffer from incomplete contractions that result in urinary retention with patients requiring using catheterization. Those affected may benefit from a combination of strain sensor and electrical stimulator to better control bladder emptying. We describe the materials and design of such a device made from thin layer carbon nanotube (CNT) and Ecoflex 00-50 and demonstrate its function with in vivo feline bladders. During bench-top characterization, the resistive and capacitive sensors exhibited reliable output throughout 5,000 stretching cycles under physiology condition. In vivo measurement with piezoresistive device showed a high correlation between sensor resistance and volume. Stimulation driven from Pt-PDMS composite electrodes successfully induced bladder contraction. We present method for reliable connection and packaging of medical grade wire to the CNT device. This work is an important step toward the translation of low-durometer elastomers, stretchable CNT percolation and Pt-PDMS composite, which are ideal for large strain bioelectric applications to sense or modulate dynamic organ states.

bioengineering↗

bioRxiv2017

Inhibition of DNA2 nuclease as a therapeutic strategy targeting replication stress in cancer cells.

Replication stress is a characteristic feature of cancer cells, which is resulted from sustained proliferative signaling induced by activation of oncogenes or loss of tumor suppressors. In cancer cells, oncogene-induced replication stress manifests as replication-associated lesions, predominantly double-strand DNA breaks (DSBs). An essential mechanism utilized by cells to repair replication-associated DSBs is homologous recombination (HR). In order to overcome replication stress and survive, cancer cells often require enhanced HR repair capacity. Therefore, the key link between HR repair and cellular tolerance to replication-associated DSBs provides us with a mechanistic rationale for exploiting synthetic lethality between HR repair inhibition and replication stress. Our studies showed that DNA2 nuclease is an evolutionarily conserved essential component of HR repair machinery. Here we demonstrate that DNA2 is indeed overexpressed in pancreatic cancers, one of the deadliest and more aggressive forms of human cancers, where mutations in the KRAS are present in 90%-95% of cases. In addition, depletion of DNA2 significantly reduces pancreatic cancer cell survival and xenograft tumor growth, suggesting the therapeutic potential of DNA2 inhibition. Finally, we develop a robust high-throughput biochemistry assay to screen for inhibitors of the DNA2 nuclease activity. The top inhibitors were shown to be efficacious against both yeast Dna2 and human DNA2. Treatment of cancer cells with DNA2 inhibitors recapitulates phenotypes observed upon DNA2 depletion, including decreased DNA end resection and attenuation of HR repair. Similar to genetic ablation of DNA2, chemical inhibition of DNA2 selectively attenuates the growth of various cancer cells with oncogene-induced replication stress. Taken together, our findings open a new avenue to develop a new class of anti-cancer drugs by targeting druggable nuclease DNA2. We 4, 16. In propose DNA2 inhibition as new strategy in cancer therapy by targeting replication stress, a molecular property of cancer cells that is acquired as a result of oncogene activation instead of targeting undruggable oncoprotein itself such as KRAS.

molecular biology↗