Biomedical subjects

Michael J Kruhlak

Publications and source records attributed to Michael J Kruhlak.

11 recordsLinked to original sources

PubMed2026

Spindle Assembly Checkpoint Competency Determines Sensitivity to KIF18A Inhibition in Small-Cell Lung Cancer.

BACKGROUND: Small-cell lung cancer (SCLC) is characterized by pervasive chromosomal instability (CIN) and remains largely refractory to targeted therapies. KIF18A, a motor protein that regulates chromosome alignment during mitosis, has emerged as a selective dependency in CIN-high tumors. Whether this dependency extends to SCLC, a prototypical CIN-high cancer, has not been established, and biomarkers predicting response to KIF18A inhibition, currently in clinical trials, are lacking. METHODS: We integrated analyses of patient tumor datasets, neuroendocrine (NE) and non- NE SCLC cell lines, and functional perturbation models to define the determinants of response to KIF18A inhibition. Chromosomal instability metrics, transcriptional programs, mitotic dynamics, and spindle assembly checkpoint (SAC) function were assessed using genomic profiling, live-cell imaging, genetic perturbation, and pharmacologic inhibition. RESULTS: KIF18A expression was elevated in SCLC tumors and correlated with CIN-associated transcriptional programs, proliferative markers, and NE status; however, these features did not predict sensitivity to KIF18A inhibition. Instead, response was determined by the functional integrity of the SAC. SAC-proficient SCLC cells underwent sustained mitotic arrest followed by apoptotic cell death upon KIF18A inhibition, whereas SAC-defective cells failed to maintain checkpoint activation and survived. Mechanistically, resistant cells exhibited impaired kinetochore recruitment of core SAC components, including MAD1 and BUBR1. Importantly, transient induction of acute CIN through MPS1 inhibition partially restored sensitivity to KIF18A inhibition in resistant models. CONCLUSIONS: This study provides the first mechanistic characterization of KIF18A dependency in SCLC, identifying SAC competency as the primary determinant of response. These findings establish a biologically informed framework for patient stratification and rational combination strategies. TRANSLATIONAL RELEVANCE: Small-cell lung cancer (SCLC) is an aggressive malignancy with few effective targeted therapies and marked chromosomal instability. KIF18A has emerged as a potential therapeutic target in genomically unstable cancers, but biomarkers predicting response to KIF18A inhibition are lacking. We demonstrate that sensitivity to KIF18A inhibition in SCLC is determined not by KIF18A expression, neuroendocrine subtype, or baseline chromosomal instability, but by the functional integrity of the spindle assembly checkpoint (SAC). SCLC cells with intact SAC signaling undergo sustained mitotic arrest and apoptosis upon KIF18A inhibition, whereas SAC-defective cells bypass checkpoint activation and survive aberrant mitosis. Notably, transient induction of acute chromosomal instability through MPS1 inhibition partially restores sensitivity in resistant models. Together, these findings identify mitotic checkpoint competency as a mechanistic determinant and candidate predictive biomarker for KIF18A-targeted therapies, providing a biologically informed framework for patient stratification and rational combination strategies relevant to ongoing KIF18A inhibitor clinical trials.

Journal Article↗

PubMed2006

Pathogenesis of Aspergillus fumigatus and the kinetics of galactomannan in an in vitro model of early invasive pulmonary aspergillosis: implications for antifungal therapy.

BACKGROUND: Little is known about the pathogenesis of invasive pulmonary aspergillosis and the relationship between the kinetics of diagnostic markers and the outcome of antifungal therapy. METHODS: An in vitro model of the human alveolus, consisting of a bilayer of human alveolar epithelial and endothelial cells, was developed. An Aspergillus fumigatus strain expressing green fluorescent protein was used. Invasion of the cell bilayer was studied using confocal and electron microscopy. The kinetics of culture, polymerase chain reaction, and galactomannan were determined. Galactomannan was used to measure the antifungal effect of macrophages and amphotericin B. A mathematical model was developed, and results were bridged to humans. RESULTS: A. fumigatus penetrated the cellular bilayer 14-16 h after inoculation. Galactomannan levels were inextricably tied to fungal invasion and were a robust measure of the antifungal effect of macrophages and amphotericin B. Neither amphotericin nor macrophages alone was able to suppress the growth of A. fumigatus; rather, the combination was required. Monte Carlo simulations showed that human dosages of amphotericin B of at least 0.6 mg/kg were required to achieve adequate drug exposure. CONCLUSIONS: This model provides a strategy by which relationships among pathogenesis, immunological effectors, and antifungal drug therapy for invasive pulmonary aspergillosis may be further understood.

Amphotericin B↗

PubMed2006

Spatio-temporal dynamics of chromatin containing DNA breaks.

The cellular response to DNA breaks consists of a complex signaling network that coordinates the initial recognition of the lesion with the induction of cell cycle checkpoints and DNA repair. With DNA wrapped around histone proteins and packaged into higher order levels of chromatin structure, the detection of a single DNA break (DSB) in the genome is the molecular equivalent of finding a needle in a haystack. A recent study from our laboratory used high-resolution electron microscropy and live cell imaging to demonstrate that chromatin undergoes a marked reorganization in response to a DSB. In an energy dependent manner, chromatin rapidly decondenses to a more open configuration in the regions surrounding the lesion. We propose that this ATP dependent chromatin-remodeling event facilitates the subsequent recognition and processing of damaged DNA. While the chromatin surrounding the lesion remodels to a more open configuration, the DNA break itself remains relatively immobile over time, consistent with the idea that DNA damage response proteins migrate to positionally stable sites of damaged DNA. The lack of significant movement of chromatin regions containing DSBs has implications for the process by which chromosomal translocations form.

Animals↗

PubMed2006

Differential expression of IFN-alpha and TRAIL/DR5 in lymphoid tissue of progressor versus nonprogressor HIV-1-infected patients.

Loss of CD4+ T cells, the hallmark of HIV pathogenesis, was suggested to be partly due to apoptosis. We recently reported that IFN-alpha produced by HIV-1-activated plasmacytoid dendritic cells (pDCs) contributes to CD4+ T cell apoptosis by the TNF-related apoptosis-inducing ligand (TRAIL)/death receptor (DR)5 pathway. Here, we show that HIV-1-induced intracellular expression of IFN-alpha in pDCs is coupled to increased expression of IFN regulatory factor 7 and MyD88 by pDCs in vivo and in vitro. Expression of IFN-alpha was increased in lymphoid tonsillar tissue (LT) of patients with progressive (HIV(prog)) compared with nonprogressive (HIV(NP)) HIV-1 disease and to uninfected controls. LT from HIV(prog) exhibited higher TRAIL and DR5 mRNA levels than LT from HIV(NP) or controls. TRAIL mRNA levels in LT correlated with plasma viral load. We show that HIV-1 induces IFN-alpha and the TRAIL/DR5 apoptotic pathway in LT, suggesting a role for these cytokines in HIV-1 immunopathogenesis.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Changes in chromatin structure and mobility in living cells at sites of DNA double-strand breaks.

The repair of DNA double-strand breaks (DSBs) is facilitated by the phosphorylation of H2AX, which organizes DNA damage signaling and chromatin remodeling complexes in the vicinity of the lesion. The disruption of DNA integrity induces an alteration of chromatin architecture that has been proposed to activate the DNA damage transducing kinase ataxia telangiectasia mutated. However, little is known about the physical properties of damaged chromatin. In this study, we use a photoactivatable version of GFP-tagged histone H2B to examine the mobility and structure of chromatin containing DSBs in living cells. We find that chromatin containing DSBs exhibits limited mobility but undergoes an energy-dependent local expansion immediately after DNA damage. The localized expansion observed in real time corresponds to a 30-40% reduction in the density of chromatin fibers in the vicinity of DSBs, as measured by energy-filtering transmission electron microscopy. The observed opening of chromatin occurs independently of H2AX and ATM. We propose that localized adenosine triphosphate-dependent decondensation of chromatin at DSBs establishes an accessible subnuclear environment that facilitates DNA damage signaling and repair.

Adenosine Triphosphate↗

PubMed2005

Selective inhibition by rottlerin of macropinocytosis in monocyte-derived dendritic cells.

We present here the analysis of fluid-phase endocytosis (FPE) in human blood monocytes and monocyte-derived dendritic cells (MDDC) facilitated by our serendipitous identification of rottlerin as an efficient inhibitor of dendritic cell FPE (IC(50) of 0.4 microM). Rottlerin was found to be an excellent tool for FPE analysis: rapid-acting, irreversible and selective for FPE (as opposed to receptor-mediated endocytosis) at concentrations of 3 microM and below. The inhibitory effect was not due to toxicity or visible change in membrane ruffles, but affects on cytoskeletal reorganization were evident in MDDC treated with relevant rottlerin concentrations during adhesion. A marked increase in FPE was observed in 1 hr interleukin (IL)-4 and granulocyte macrophage-colony stimulating factor (GM-CSF)-stimulated monocytes. Moreover, rottlerin inhibited the augmented FPE of 1-day cytokine treated monocytes and their augmented ability to induce T cell proliferative responses to tetanus toxoid. We conclude that rottlerin is a useful tool for investigating FPE and its functional importance.

Acetophenones↗

PubMed2004

Rac1 mediates collapse of microvilli on chemokine-activated T lymphocytes.

Lymphocytes circulate in the blood and upon chemokine activation rapidly bind, where needed, to microvasculature to mediate immune surveillance. Resorption of microvilli is an early morphological alteration induced by chemokines that facilitates lymphocyte emigration. However, the antecedent molecular mechanisms remain largely undefined. We demonstrate that Rac1 plays a fundamental role in chemokine-induced microvillar breakdown in human T lymphocytes. The supporting evidence includes: first, chemokine induces Rac1 activation within 5 s via a signaling pathway that involves Galphai. Second, constitutively active Rac1 mediates microvilli disintegration. Third, blocking Rac1 function by cell permeant C-terminal "Trojan" peptides corresponding to Rac1 (but not Rac2, Rho, or Cdc42) blocks microvillar loss induced by the chemokine stromal cell-derived factor 1alpha (SDF-1alpha). Furthermore, we demonstrate that the molecular mechanism of Rac1 action involves dephosphorylation-induced inactivation of the ezrin/radixin/moesin (ERM) family of actin regulators; such inactivation is known to detach the membrane from the underlying actin cytoskeleton, thereby facilitating disassembly of actin-based peripheral processes. Specifically, ERM dephosphorylation is induced by constitutively active Rac1 and stromal cell-derived factor 1alpha-induced ERM dephosphorylation is blocked by either the dominant negative Rac1 construct or by Rac1 C-terminal peptides. Importantly, the basic residues at the C terminus of Rac1 are critical to Rac1's participation in ERM dephosphorylation and in microvillar retraction. Together, these data elucidate new roles for Rac1 in early signal transduction and cytoskeletal rearrangement of T lymphocytes responding to chemokine.

Actins↗

PubMed2004

TLR9 is localized in the endoplasmic reticulum prior to stimulation.

In mammals, 10 TLRs recognize conserved pathogen-associated molecular patterns, resulting in the induction of inflammatory innate immune responses. One of these, TLR9, is activated intracellularly by bacterial DNA and synthetic oligodeoxynucleotides (ODN), containing unmethylated CpG dinucleotides. Following treatment with CpG ODN, TLR9 is found in lysosome-associated membrane protein type 1-positive lysosomes, and we asked which intracellular compartment contains TLR9 before CpG exposure. Surprisingly, we found by microscopy and supporting biochemical evidence that both transfected and endogenously expressed human TLR9 is retained in the endoplasmic reticulum. By contrast, human TLR4 trafficked to the cell surface, indicating that endoplasmic reticulum retention is not a property common to all TLRs. Because TLR9 is observed in endocytic vesicles following exposure to CpG ODN, our data indicate that a special mechanism must exist for translocating TLR9 to the signaling compartments that contain the CpG DNA.

Activating Transcription Factor 3↗

PubMed2003

Mast cell degranulation requires N-ethylmaleimide-sensitive factor-mediated SNARE disassembly.

Mast cells possess specialized granules that, upon stimulation of surface FcR with IgE, fuse with the plasma membrane, thereby releasing inflammatory mediators. A family of membrane fusion proteins called SNAREs, which are present on both the granule and the plasma membrane, plays a role in the fusion of these granules with the plasma membrane of mast cells. In addition to the SNAREs themselves, it is likely that the SNARE accessory protein, N-ethylmaleimide-sensitive factor (NSF), affects the composition and structure of the SNARE complex. NSF is a cytoplasmic ATPase that disassembles the SNARE complexes. To investigate the role of NSF in mast cell degranulation, we developed an assay to measure secretion from transiently transfected RBL (rat basophilic leukemia)-2H3 mast cells (a tumor analog of mucosal mast cells). RBL-2H3 cells were cotransfected with a plasmid encoding a human growth hormone secretion reporter along with either wild-type NSF or an NSF mutant that lacks ATPase activity. Human growth hormone was targeted to and released from secretory granules in RBL-2H3 cells, and coexpression with mutant NSF dramatically inhibited regulated exocytosis from the transfected cells. Biochemical analysis of SNARE complexes in these cells revealed that overexpression of the NSF mutant decreased disassembly and resulted in an accumulation of SNARE complexes. These data reveal a role for NSF in mast cell exocytosis and highlight the importance of SNARE disassembly, or priming, in regulated exocytosis from mast cells.

Adenosine Triphosphatases↗

PubMed2003

Histone H2AX phosphorylation is dispensable for the initial recognition of DNA breaks.

Histone H2AX is rapidly phosphorylated in the chromatin micro-environment surrounding a DNA double-strand break (DSB). Although H2AX deficiency is not detrimental to life, H2AX is required for the accumulation of numerous essential proteins into irradiation induced foci (IRIF). However, the relationship between IRIF formation, H2AX phosphorylation (gamma-H2AX) and the detection of DNA damage is unclear. Here, we show that the migration of repair and signalling proteins to DSBs is not abrogated in H2AX(-/-) cells, or in H2AX-deficient cells that have been reconstituted with H2AX mutants that eliminate phosphorylation. Despite their initial recruitment to DSBs, numerous factors, including Nbs1, 53BP1 and Brca1, subsequently fail to form IRIF. We propose that gamma-H2AX does not constitute the primary signal required for the redistribution of repair complexes to damaged chromatin, but may function to concentrate proteins in the vicinity of DNA lesions. The differential requirements for factor recruitment to DSBs and sequestration into IRIF may explain why essential regulatory pathways controlling the ability of cells to respond to DNA damage are not abolished in the absence of H2AX.

Animals↗

PubMed2003

Same serial section correlative light and energy-filtered transmission electron microscopy.

Correlative imaging of a specific cell with both the light microscope and the electron microscope has proved to be a difficult task, requiring enormous amounts of patience and technical skill. We describe a technique with a high rate of success, which can be used to identify a particular cell in the light microscope and then to embed and thin-section it for electron microscopy. The technique also includes a method to obtain many uninterrupted, thin serial sections for imaging by conventional or energy-filtered transmission electron microscopy, to obtain images for 3D analysis of detail at the suborganelle level.

Fluorescent Antibody Technique↗