Stephanie D. Drenning

Requirement of Stat3 but not Stat1 activation for epidermal growth factor receptor- mediated cell growth In vitro.

Stimulation of epidermal growth factor receptor (EGFR) by ligand(s) leads to activation of signaling molecules including Stat1 and Stat3, two members of the signal transducers and activators of transcription (STAT) protein family. Activation of Stat1 and Stat3 was constitutive in transformed squamous epithelial cells, which produce elevated levels of TGF-alpha, and was enhanced by the addition of exogenous TGF-alpha. Targeting of Stat3 using antisense oligonucleotides directed against the translation initiation site, resulted in significant growth inhibition. In addition, cells stably transfected with dominant negative mutant Stat3 constructs failed to proliferate in vitro. In contrast, targeting of Stat1 using either antisense or dominant-negative strategies had no effect on cell growth. Thus, TGF-alpha/EGFR-mediated autocrine growth of transformed epithelial cells is dependent on activation of Stat3 but not Stat1.

Epidermal growth factor receptor--mediated stat3 signaling blocks apoptosis in head and neck cancer.

Objectives Upregulation of epidermal growth factor receptor (EGFR) is critical for the loss of growth control in a variety of human cancers including squamous cell cancers of the head and neck (SCCHN). In these tumor cells in culture, EGFR stimulation initiates signaling via persistent activation of STAT proteins, particularly Stat3. The present study was conducted to study the association between EGFR stimulation and constitutive activation of Stat3 in SCCHN in vivo and to investigate the proliferative and apoptotic consequences of Stat3 downmodulation in SCCHN cells in vitro.

STAPHYLOCOCCUS AUREUS NASAL COLONIZATION AND ASSOCIATION WITH INFECTIONS IN LIVER TRANSPLANT RECIPIENTS

BACKGROUND Staphylococcus aureus has emerged as a leading cause of bacterial infections after liver transplantation. However, the role of nasal colonization in the development of S aureus infections has never been explored in liver transplant recipients. The objectives of this study were to determine whether nasal carriage of S aureus was a risk factor for S aureus infections in liver transplant recipients. METHODS Over a 2-year period, 30 consecutive liver transplant recipients were studied. Beginning when the recipients were transplant candidates, nasal cultures were performed at each admission and monthly thereafter until discharge or death. RESULTS Overall, 67% (20/30) of the patients were nasal carriers, 70% of the carriers had methicillin-resistant S aureus (MRSA), 15% had methicillin-sensitive S aureus, and 15% had both MRSA and methicillin-sensitive S aureus. Infections were significantly associated with the carrier state; 100% (9/9) of the infected patients were carriers as compared with 50% (11/21) of the noninfected patients (P=0.01). All infections were a result of MRSA, and 56% (5/9) of the infections were bacteremia. Median time to the onset of S aureus infections was 16 days after transplant. Pulse field gel electrophoresis (with digestion of S aureus with SmaI restriction enzyme) in seven infected patients demonstrated that the isolates from the anterior nares matched the invasive isolates in all cases. A total of 43% (3/7) of these infected patients shared the same restriction pattern. CONCLUSION MRSA colonization of the anterior nares was a significant predictor of MRSA infections in liver transplant recipients. Infections occurred only in those colonized with MRSA and were a result of the endogenously colonizing S aureus strains in all cases.

Differential function of STAT5 isoforms in head and neck cancer growth control.

Up-regulation of the epidermal growth factor receptor (EGFR) is critical for the loss of growth control in a variety of human cancers, including squamous cell carcinoma of the head and neck (SCCHN). Stimulation of EGFR results in activation of mitogenic signaling pathways including Signal Transducers and Activators of Transcription (STATs). Stat5 activation has been primarily demonstrated in hematopoietic malignancies. Gene disruption studies suggest potentially distinct functions of the Stat5 isoforms, Stat5a and Stat5b, which are encoded by two genes closely linked on human chromosome 17. To determine the function of Stat5 in SCCHN growth control, we studied the expression and constitutive activation of Stat5a and Stat5b in normal and transformed human squamous epithelial cells. Increased constitutive activation of Stat5 was detected in transformed compared with normal squamous cells. Blockade of TGF-α or EGFR, abrogated Stat5 activation. Targeting of Stat5b using antisense oligonucleotides inhibited SCCHN growth. In addition, SCCHN cells stably transfected with dominant negative mutant Stat5b failed to proliferate in vitro. In contrast, targeting of Stat5a using either antisense or dominant negative strategies had no effect on cell growth. These results suggest that TGF-α/EGFR-mediated autocrine growth of transformed epithelial cells is dependent on activation of Stat5b but not Stat5a.

TGF-α antisense gene therapy inhibits head and neck squamous cell carcinoma growth in vivo

Unlike normal mucosal squamous epithelial cells, head and neck squamous cell carcinomas (HNSCCs) overexpress TGF-α mRNA and protein which is required to sustain the proliferation of HNSCC cells in vitro. To determine whether TGF-α expression contributes to tumor growth in vivo, cationic liposome-mediated gene transfer was used to deliver an antisense expression construct targeting the human TGF-α gene into human head and neck tumor cells, grown as subcutaneous xenografts in nude mice. The TGF-α antisense gene was immediately detected in the cytoplasm of the tumor cells, translocated to the nucleus by 12 h and remained localized to the nucleus for up to 3 days. Direct inoculation of the TGF-α antisense (but not the corresponding sense) construct into established HNSCC tumors resulted in inhibition of tumor growth. Sustained antitumor effects were observed for up to 1 year after the treatments were discontinued. Down-modulation of TGF-α was accompanied by increased apoptosis in vivo. These experiments indicate that interference with the TGF-α/EGFR autocrine signaling pathway may be an effective therapeutic strategy for cancers which overexpress this ligand/receptor pair.

Unexpected Similarity of Pulsed-Field Gel Electrophoresis Patterns of Unrelated Clinical Isolates of Legionella pneumophila, Serogroup 1

Phenotypic and genotypic methods identify subtypes of Legionella pneumophila, serogroup 1, and match patient and environmental isolates from suspected sources. The strength of this association is limited by the lack of information regarding the frequency and distribution of isolates belonging to various subtypes. In this study, 62 clinical isolates of L. pneumophila, serogroup 1, were subtyped by using pulsed-field gel electrophoresis (PFGE), to determine the distribution and degree of diversity of PFGE patterns among monoclonal antibody (MAb) subtypes. Unexpectedly, 8 of 21 MAb Philadelphia 1 isolates had a common PFGE pattern, and, among 12 MAb OLDA isolates, only 2 PFGE patterns were seen. Our hypothesis was that PFGE patterns were distributed randomly; however, statistical analysis showed that the distribution of subtypes was not random (Fishers exact test 0.13; P>.05). In light of these results, researchers who do epidemiological investigations should use caution when interpreting the significance of matching PFGE patterns of L. pneumophila, serogroup 1.

IL-12 receptor-mediated upregulation of FasL in human ovarian carcinoma cells

The expression and functions of IL‐12 receptor (IL‐12R) in human ovarian carcinoma cell lines have been investigated. Ovarian carcinoma cells express both the IL‐12Rβ1 and the IL‐12Rβ2 subunits. IL‐12R crosslinking resulted in phosphorylation of Tyk2, p44 (ERK1) and Akt kinases and activation of STATs 2, 3, 4 and 5. IL‐12 induced substantial upregulation of Fas ligand (FasL) surface expression in ovarian carcinoma cells paralleled by an increased ability to induce apoptosis in Jurkat cells and PHA‐activated lymphocytes. The induction of surface expression of FasL by IL‐12 was not due to upregulation of FasL gene expression, but resulted from downregulation of matrix metalloproteinases (MMPs)‐3 and ‐7 and consequently reduced cleavage of FasL from the cell surface. These findings bring new insights into the significance of IL‐12‐mediated effects in nonlymphoid cancer cells that might be of importance for improving the design of IL‐12‐based therapies for ovarian cancer.