Biomedical subjects

J T Parsons

Publications and source records attributed to J T Parsons.

At least 109 records · Page 6Linked to original sources

PubMed1996

Does neck stage predict local control after irradiation for head and neck cancer?

The impact of neck stage (N stage) on local control after treatment for head and neck cancer is controversial. This article reviews the pertinent literature. Based on this review, the authors conclude that although N stage may be inversely related to local control, the relationship is relatively weak. Hence, current data are insufficient to justify altering treatment of the primary lesion based solely on N stage.

Head and Neck Neoplasms↗

PubMed1996

Response of the normal eye to high dose radiotherapy.

Radiation therapy of tumors near the eye or optic nerves often requires incidental irradiation of these structures, even when they are not clinically involved by tumor. Depending on the radiation treatment volume and dose required, radiation injury to the lens, lacrimal apparatus, retina, or optic nerve may result. The time to expression and severity of injury are dose-dependent. This paper reviews the results of 157 patients who were followed for a minimum of 3 years after radiotherapy for primary extracranial tumors at the University of Florida, in which the lacrimal gland, lens, retina, and/or optic nerve(s) received irradiation. This review shows that, after treatment at approximately 1.8 to 2.0 Gy per fraction, the incidence of severe dry-eye syndrome, retinopathy, and optic neuropathy appears to increase steeply after doses of 40, 50, and 60 Gy, respectively.

Dose-Response Relationship, Radiation↗

PubMed1995

Testicular seminoma: a failure analysis and literature review.

PURPOSE: A retrospective analysis of 74 patients with pure seminoma, treated at the University of Florida between 1964 and 1989, was undertaken. METHODS AND MATERIALS: All patients received megavoltage irradiation, with chemotherapy reserved for salvage. At 10 years, the probability of relapse-free survival was 91% for Stage I, 93% for Stage IIA, 83% for Stage IIB, and 75% for Stage III patients. RESULTS: There were seven recurrences, none of which occurred in irradiated areas. Only two of seven patients (29%) with recurrence were salvaged. CONCLUSION: A literature review revealed an increasing rate of mediastinal or supraclavicular recurrence, correlating with the size of the subdiaphragmatic disease, in Stage II patients who did not receive elective mediastinal irradiation. Recommendations are made regarding the role of elective mediastinal irradiation for Stage II disease. We conclude that patients with Stage I or II seminoma can have high cure rates when treated with radiotherapy alone. Patients with Stage III seminoma should be treated initially with cisplatin-based chemotherapy.

Adult↗

PubMed1995

Interaction of focal adhesion kinase with cytoskeletal protein talin.

The interaction of cells with extracellular matrix proteins plays a critical role in a variety of biological processes. Recent studies suggest that cell-matrix interactions mediated by integrins can transduce biochemical signals to the cell interior that regulate cell proliferation and differentiation. These studies have placed the focal adhesion kinase (FAK), an intracellular protein tyrosine kinase, in a central position in integrin-initiated signal transduction pathways (Zachary, I., and Rozengurt, E. (1992) Cell 71, 891-894; Schaller, M., and Parsons, J. T. (1993) Trends Cell Biol. 3, 258-262). Here, we report data suggesting a possible association of FAK with the cytoskeletal protein talin in NIH 3T3 cells. We have identified a 48-amino acid sequence in the carboxyl-terminal domain of FAK necessary for talin binding in vitro. Furthermore, we have correlated the ability of integrin to induce FAK phosphorylation with its ability to bind talin using a mutant integrin lacking the carboxyl-terminal 13 amino acids. These studies suggest talin may be a mediator for FAK activation in signaling initiated by integrins and may provide an explanation for the dependence on the integrity of actin-cytoskeleton of multiple intracellular signaling pathways converging to FAK activation and autophosphorylation.

3T3 Cells↗

PubMed1995

Salvage surgery following radiation failure in squamous cell carcinoma of the supraglottic larynx.

PURPOSE: We analyzed the clinical course of patients who developed local (primary) recurrence following high-dose irradiation of squamous cell carcinoma of the supraglottic larynx. METHODS AND MATERIALS: Between October 1964 and July 1991, 206 patients with previously untreated squamous cell carcinoma of the supraglottic larynx underwent radiotherapy with curative intent. Local failure occurred in 46 (22%) patients. Successful surgical salvage was defined as no evidence of recurrent cancer for at least 2 years after salvage surgery and continuously thereafter. RESULTS: Sixteen patients did not undergo salvage surgery because of refusal (7 patients), severe medical illness (2 patients), concurrent distant metastasis (5 patients), or unresectable neck disease (2 patients). Twenty-six patients underwent total laryngectomy, and 4 patients had a voice-sparing procedure. Successful salvage was achieved in 50% of patients who underwent surgery. The rate of successful salvage did not correlate with preirradiation T-stage or time to failure after irradiation. Most of the failures after surgery were because of failure to control the primary cancer. The overall rate of postsurgical complications was 37%. No operative or perioperative deaths occurred. The 5-year survival rate for all 46 patients, calculated from the date of irradiation failure, was 20%, while the 5-year survival rate after salvage surgery for the 30 patients who underwent the procedure was 29%. CONCLUSION: There are few data in the literature regarding the clinical outcome in patients whose tumors are not controlled by initial radiotherapy. In the current and previous series, one-half to two-thirds of patients who developed primary failure underwent salvage surgery, which was successful in approximately half of the operated patients, leading to a 25-30% rate of long-term disease-free survival among the entire group of patients who developed failure.

Adult↗

PubMed1995

Signal transduction through integrins: a central role for focal adhesion kinase?

The integrins are receptors for proteins of the extracellular matrix, both providing a physical link to the cytoskeleton and transducing signals from the extracellular matrix. Activation of integrins leads to tyrosine and serine phosphorylation of a number of proteins, elevation of cytosolic calcium levels, cytoplasmic alkalinization, changes in phospholipid metabolism and, ultimately, changes in gene expression. The recently discovered focal adhesion kinase localizes to focal contacts, which are sites of integrin clustering, and focal adhesion kinase can physically associate with integrins in vitro. As integrins lack intrinsic catalytic activity, focal adhesion kinase is a candidate for a signaling molecule that is recruited by integrins in order to trigger the generation of intracellular second messengers. Thus, focal adhesion kinase may play a central role in signal transduction through integrins.

Cell Adhesion↗

PubMed1995

Bladder-sparing multimodality treatment of muscle-invasive bladder cancer: a five-year follow-up.

OBJECTIVES: To determine the long-term results of a bladder-sparing approach in the treatment of muscle-invasive bladder cancer. METHODS: Ninety-four patients with invasive transitional cell carcinoma of the bladder were treated by transurethral resection followed by 2 or 3 cycles of cisplatin-based chemotherapy. Patients were then treated with 6480 cGy of radiation in 49 patients, segmental cystectomy in 8, or surveillance only in 7. Patients who failed to respond to chemotherapy or radiation therapy, or who developed recurrent muscle-invasive disease in follow-up, underwent salvage cystectomy. Patients were then carefully followed for a median follow-up of more than 5 years. RESULTS: After initial therapy, 53 patients (56%) were alive with their bladder preserved. Thirty of those 53 (57%) developed a local recurrence in follow-up. After a median follow-up of more than 5 years, the ultimate relapse-free survival is 49% (Stage T2, 84%; T3, 53%; and T4, 11%; P < 0.01). Of all patients enrolled, 53% had bladder preservation; however, of the currently surviving patients, 16 of 39 (41%) have their bladders intact (T2, 50%; T3, 37%; T4, 0%). Only 18% of the initially enrolled population is alive with a preserved bladder. The 5-year survival of patients who had cystectomy at some point during the study, compared with those who have had their bladders preserved, was 65% versus 40%, respectively (P < 0.01). CONCLUSIONS: Our long-term results with multimodality therapy with attempted bladder preservation showed no definitive improvement in survival compared with modern series of cystectomy alone, and a disappointingly low rate of disease-free bladder preservation. We found a high rate of locally recurrent disease in the preserved bladders. We also noted a decrease in survival in our patients with bladder preservation compared with those without preservation. Bladder preservation, although possible, should be limited to a very select group of patients.

Aged↗

PubMed1995

Radiotherapy in the management of temporal bone chemodectoma.

Forty patients with 42 temporal bone chemodectomas were treated with radiotherapy alone (37 tumors) or subtotal resection and irradiation (5 tumors) at the University of Florida between 1968 and 1992. Thirty-three lesions were previously untreated, whereas 9 had undergone prior treatment (surgery, 6 lesions; radiotherapy, 1 lesion; or both, 2 lesions) and were treated for locally recurrent disease. All 3 patients who received prior radiotherapy had been treated at other institutions. Patients had minimum follow-up times as follows: 2 years, 40 patients (100%); 5 years, 31 patients (78%); 10 years, 21 patients (53%); 15 years, 16 patients (40%); 20 years, 9 patients (23%); and 25 years, 2 patients (5%). The local control rate at 20 years, calculated by the Kaplan-Meier product-limit method for the overall group of 42 lesions, was 89%. The likelihood of cause-specific survival at 20 years was 94%. The incidence of treatment-related complications was acceptable. We conclude that irradiation offers a high probability of tumor control with relatively minimal risks for patients with chemodectomas of the temporal bone.

Journal Article↗

PubMed1995

Focal adhesion kinase and paxillin bind to peptides mimicking beta integrin cytoplasmic domains.

The integrins have recently been implicated in signal transduction. A likely mediator of integrin signaling is focal adhesion kinase (pp125FAK or FAK), a structurally distinct protein tyrosine kinase that becomes enzymatically activated upon engagement of integrins with their ligands. A second candidate signaling molecule is paxillin, a focal adhesion associated, cytoskeletal protein that coordinately becomes phosphorylated on tyrosine upon activation of pp125FAK. Paxillin physically complexes with two protein tyrosine kinases, pp60src and Csk (COOH-terminal src kinase), and the oncoprotein p47gag-crk, each of which could function as part of a paxillin signaling complex. Using an in vitro assay we have established that the cytoplasmic domain of the beta 1 integrin can bind to paxillin and pp125FAK from chicken embryo cell lysates. The NH2-terminal, noncatalytic domain of pp125FAK can bind directly to the cytoplasmic tail of beta 1 and recognizes integrin sequences distinct from those involved in binding to alpha-actinin. Paxillin binding is independent of pp125FAK binding despite the fact that both bind to the same region of beta 1. These results demonstrate that the cytoplasmic domain of the beta subunits of integrins contain binding sites for both signaling molecules and structural proteins suggesting that integrins can coordinate the generation of cytoplasmic signals in addition to their role in anchoring components of the cytoskeleton.

Actinin↗

PubMed1995

Paxillin, a tyrosine phosphorylated focal adhesion-associated protein binds to the carboxyl terminal domain of focal adhesion kinase.

Focal adhesion kinase (pp125FAK or FAK) and paxillin colocalize with integrins in structures called focal adhesions. pp125FAK plays an important role in the transmission of integrin-induced cytoplasmic signals. Paxillin has also been implicated in cell signaling by virtue of its association with the protein tyrosine kinases pp60src and Csk (C-terminal Src kinase) as well as with the adapter/oncoprotein p47gag-crk. In this report we show that endogenous pp125FAK and paxillin form a stable complex both in vivo and in vitro and that this interaction is direct, requiring only pp125FAK and paxillin. The paxillin binding site on pp125FAK has been localized to the carboxy-terminal 148 residues of pp125FAK, but appears to be distinct from the previously identified focal adhesion-targeting sequence also present in the carboxy-terminal domain of pp125FAK. The interaction of paxillin and pp125FAK is independent of the adhesion of cells to the extracellular matrix, as the association can be detected in suspension cells as well as those attached to fibronectin.

Animals↗

PubMed1995

pp125FAK-dependent tyrosine phosphorylation of paxillin creates a high-affinity binding site for Crk.

Paxillin, a focal-adhesion-associated protein, becomes phosphorylated in response to a number of stimuli which also induce the tyrosine phosphorylation of the focal-adhesion-associated protein tyrosine kinase pp125FAK. On the basis of their colocalization and coordinate phosphorylation, paxillin is a candidate for a substrate of pp125FAK. We describe here conditions under which the phosphorylation of paxillin on tyrosine is pp125FAK dependent, supporting the hypothesis that paxillin phosphorylation is regulated by pp125FAK. pp125FAK must localize to focal adhesions and become autophosphorylated to induce paxillin phosphorylation. Phosphorylation of paxillin on tyrosine creates binding sites for the SH2 domains of Crk, Csk, and Src. We identify two sites of phosphorylation as tyrosine residues 31 and 118, each of which conforms to the Crk SH2 domain binding motif, (P)YXXP. These observations suggest that paxillin serves as an adapter protein, similar to insulin receptor substrate 1, and that pp125FAK may regulate the formation of signaling complexes by directing the phosphorylation of paxillin on tyrosine.

Amino Acid Sequence↗

PubMed1995

Adhesion-induced tyrosine phosphorylation of the p130 src substrate.

Adhesion of cells to the extracellular matrix leads to an increase in the tyrosine phosphorylation of a specific set of proteins, three of which have now been identified as the focal adhesion proteins pp125FAK, paxillin and tensin. In addition, we have previously noted the adhesion-induced tyrosine phosphorylation of a fourth protein, with an apparent molecular mass of 130. As in the case of FAK, paxillin and tensin, a 130 kDa protein is also found to be highly tyrosine phosphorylated in Rous sarcoma virus (RSV)-transformed cells. This protein forms a stable complex with pp60src and is directly phosphorylated by activated forms of c-src. Using a monoclonal antibody (mAb 4F4) specific for the src-associated p130 we show that p130 is also phosphorylated in response to cell adhesion. Immunoprecipitation of p130 followed by an anti-phosphotyrosine immunoblot revealed that adhesion of rat embryo fibroblasts (REF52) to fibronectin (FN) led to a significant increase in the phosphotyrosine content of p130. Furthermore, a comparison of cell lysates before and after immunoprecipitation confirmed the absence of tyrosine phosphorylated p130 from lysates immunoprecipitated with mAb 4F4. Immunofluorescence staining of REF52s revealed that p130 is found in focal adhesions as well as along stress fibers in a pattern reminiscent of that exhibited by alpha-actinin. In addition, in many cells, we found significant staining in the nucleus, but evidence is presented that the nuclear staining is not due to tyrosine phosphorylated p130. Finally, unlike pp125FAK, p130 does not appear to be itself a kinase as evidence by immune-complex kinase assays carried out in the presence or absence of exogenous substrates.

Animals↗

PubMed1995

Nasal mucociliary clearance after radiation therapy.

Irradiation has been demonstrated to cause decreased mucociliary clearance in animal models. We sought to verify this effect clinically by using the saccharin transport test to evaluate nasal mucociliary clearance in 9 patients previously treated with radiation therapy to the nasal cavity. The patients also completed a questionnaire examining the prevalence of nasal symptoms before and after radiation therapy. Patients who received radiation therapy had no clearance of saccharin from the nasal cavity at a minimum of 20 minutes. The controls had a median clearance time of 5 minutes. The patients noted a higher prevalence of nasal congestion, drainage, and facial pain after radiation therapy. This study demonstrates that radiation therapy to the nasal cavity causes a decrease in nasal mucociliary clearance. This alteration should be considered when selecting therapy for malignancies in the nasal area.

Administration, Intranasal↗

PubMed1995

Radiation therapy for sinus malignancies.

Primary tumors arising in the nasal cavity and paranasal sinuses usually are considered together. Except in the nasal cavity, where occasional lesions present early because of nasal obstruction, most lesions are advanced at presentation, and the exact site of origin may be uncertain. Radiation therapy may be used alone or in combination with surgery in the management of patients with squamous cell carcinoma of these sites.

Aged↗

PubMed1994

Radiation optic neuropathy after megavoltage external-beam irradiation: analysis of time-dose factors.

PURPOSE: To investigate the risk of radiation-induced optic neuropathy according to total radiotherapy dose and fraction size, based on both retrospective and prospectively collected data. METHODS AND MATERIALS: Between October 1964 and May 1989, 215 optic nerves in 131 patients received fractionated external-beam irradiation during the treatment of primary extracranial head and neck tumors. All patients had a minimum of 3 years of ophthalmologic follow-up (range, 3 to 21 years). The clinical end point was visual acuity of 20/100 or worse as a result of optic nerve injury. RESULTS: Anterior ischemic optic neuropathy developed in five nerves (at mean and median times of 32 and 30 months, respectively, and a range of 2-4 years). Retrobulbar optic neuropathy developed in 12 nerves (at mean and median times of 47 and 28 months, respectively, and a range of 1-14 years). No injuries were observed in 106 optic nerves that received a total dose of < 59 Gy. Among nerves that received doses of > or = 60 Gy, the dose per fraction was more important than the total dose in producing optic neuropathy. The 15-year actuarial risk of optic neuropathy after doses of > or = 60 Gy was 11% when treatment was administered in fraction sizes of < 1.9 Gy, compared with 47% when given in fraction sizes of > or = 1.9 Gy. The data also suggest an increased risk of optic nerve injury with increasing age. CONCLUSION: As there is no effective treatment of radiation-induced optic neuropathy, efforts should be directed at its prevention by minimizing the total dose, paying attention to the dose per fraction to the nerve, and using reduced-field techniques where appropriate to limit the volume of tissues that receive high-dose irradiation.

Adolescent↗

PubMed1994

Radiation retinopathy after external-beam irradiation: analysis of time-dose factors.

PURPOSE: To investigate the risk of radiation-induced retinopathy according to total radiation dose and fraction size, based on both retrospective and prospectively collected data. METHODS AND MATERIALS: Between October 1964 and May 1989, 68 retinae in 64 patients received fractionated external-beam irradiation during the treatment of primary extracranial head and neck tumors. All patients had a minimum of 3 years of ophthalmologic follow-up (range, 3 to 26 years; mean, 9 years; median, 8 years). RESULTS: Twenty-seven eyes in 26 patients developed radiation retinopathy resulting in visual acuity of 20/200 or worse. The mean and median times to the onset of symptoms attributable to retinal ischemia were 2.8 and 2.5 years, respectively. Fourteen of the injured eyes developed rubeosis iridis and/or neovascular glaucoma. Radiation retinopathy was not observed at doses below 45 Gy, but increased steadily in incidence at doses > or = 45 Gy. In the range of doses between 45 and 55 Gy, there was an increased risk of injury among patients who received doses per fraction of > or = 1.9 Gy (p = .09). There was also a trend toward increased risk of injury among patients who received chemotherapy (two of two vs. four of ten in the 45-51 Gy range; p = .23). The lowest dose associated with retinopathy was 45 Gy delivered to a diabetic patient by twice-a-day fractionation. The data did not suggest an increased risk of radiation retinopathy with increasing age. CONCLUSION: The current study suggests the importance of total dose as well as dose per fraction, and adds support to a small body of literature suggesting that patients with diabetes mellitus or who receive chemotherapy are at increased risk of injury. A sigmoid dose-response curve is constructed from our current data and data from the literature.

Adolescent↗

PubMed1994

Severe dry-eye syndrome following external beam irradiation.

PURPOSE: There are limited data in the literature on the probability of dry-eye complications according to radiotherapy dose. This study investigates the risk of radiation-induced severe dry-eye syndrome in patients in whom an entire orbit was exposed to fractionated external beam irradiation. METHODS AND MATERIALS: Between October 1964 and May 1989, 33 patients with extracranial head and neck tumors received irradiation of an entire orbit. Most patients were treated with 60Co. The dose to the lacrimal apparatus was calculated at a depth of 1 cm from the anterior skin surface, the approximate depth of the major lacrimal gland. The end point of the study was severe dry-eye syndrome sufficient to produce visual loss secondary to corneal opacification, ulceration, or vascularization. RESULTS: Twenty patients developed severe dry-eye syndrome. All 17 patients who received doses > or = 57 Gy developed severe dry-eye syndrome. Three (19%) of 16 patients who received doses < or = 45 Gy developed severe dry-eye syndrome; injuries in the latter group were much slower to develop (4 to 11 years) than in the higher dose group, in whom corneal vascularization and opacification were usually pronounced within 9-10 months. There were no data for the range of doses between 45.01 and 56.99 Gy. The data did not suggest an increased risk of severe dry-eye syndrome with increasing age. CONCLUSION: Data from the current series and the literature are combined to construct a sigmoid dose response curve. The incidence of injury increases from 0% reported after doses < or = 30 Gy to 100% after doses > or = 57 Gy.

Adolescent↗

PubMed1994

SH2 domain specificity and activity modified by a single residue.

Many intracellular targets of protein-tyrosine kinases possess Src homology 2 (SH2) domains that directly recognize phosphotyrosine-containing sites on autophosphorylated growth factor receptors and cytoplasmic proteins, and thereby mediate the activation of biochemical signalling pathways. SH2 domains possess relatively well conserved residues that form the phosphotyrosine-binding pocket, and more variable residues that are implicated in determining binding specificity by recognition of the three amino acids carboxy-terminal to phosphotyrosine (the +1 to +3 positions). One such residue, occupying the EF1 position of the +3-binding pocket, is a Thr in the SH2 domain of the Src tyrosine kinase, but is predicted to be a Trp in the SH2 domain of the Sem-5/drk/Grb2 adaptor protein. Here we report that changing this residue in the Src SH2 domain from Thr to Trp switches its selectivity to resemble that of the Sem-5/drk/Grb2 SH2 domain. Furthermore, this mutant Src SH2 domain effectively substitutes for the SH2 domain of the Sem-5 protein in activation of the Ras pathway in vivo. These results identify a residue that can modify SH2 selectivity, and indicate that the biological activity of an SH2 domain correlates with its binding specificity.

Adaptor Proteins, Signal Transducing↗