Abstract

The objective of this study was to examine the role of gap junctions in the radiation resistance of thyroid follicles. The question of whether gap junctional intercellular communication plays an important role in the “contact effect”, wherein cells in direct apposition are more resistant to the damaging effects of radiation, has been debated for years. We used the Fischer rat thyroid cell line (FRTL-5) to carry out our experiments. This thesis is divided into two parts: 1) characterization of gap junctional properties in FRTL-5 cells and, 2) exposure of these cells to radiation.

We found that, unlike primary thyroid cells, FRTL-5 cells do not express Cx43 or Cx26 at the mRNA or protein level. Gap junctional intercellular communication in these cells, established as follicles, is provided by Cx32. In addition, we found that after being continuously passaged (more than 17 times), Cx32 gap junctions failed to transfer dye and were immuno-undetectable. This may be caused by a genetic alteration of one base shift in the middle of cytoplasmic loop coding region and the aberrant C-terminus of the Cx32 sequence (obtained from RT-PCR). The non-functional Cx32 FRTL-5 (late) cultures showed an uncontrolled growth rate. Their doubling time was only half of the functional Cx32 cultures (early). T4 production in the late FRTL-5 cultures was about 25 percent reduced when compared with the early cultures.

Early and late FRTL-5 follicular cultures were exposed to gamma rays or proton beams delivered over a range of physical doses. In terms of radiation quality-based differences, the late cultures showed no significant differences in response to proton and gamma radiation, whereas, early cultures showed a greater loss of viability by proton radiation. This was evident in the a-components of cell viability curves. The higher a value of the proton viability curve showed that proton irradiated early cultures were less resistant to killing and/or less efficient in repairing damage than gamma irradiated early cultures. The proton radiation showed no significant differences amongst the cell cultures regardless of Cx32 expression. However, there was a significant difference in these cultures in response to gamma radiation. The flatter shoulder (lower a value) of the gamma viability curve of the early culture suggested a greater repair efficiency and/or more resistant to killing. We conclude that the functional Cx32 gap junction does enhance radiation resistance to thyroid cells established as follicles.

LLU Discipline

Microbiology and Molecular Genetics

Department

Microbiology

School

Graduate School

First Advisor

Lora M. Green

Second Advisor

Carlos Casiano

Third Advisor

Daila Gridley

Fourth Advisor

Gregory A. Nelson

Degree Name

Master of Science (MS)

Degree Level

M.S.

Year Degree Awarded

2000

Date (Title Page)

9-2000

Language

English

Library of Congress/MESH Subject Headings

Connexins; Radiation-Protective Agents; Radiation, Ionizing; Thyroid Neoplasm -- radiotherapy.

Type

Thesis

Page Count

xii; 85

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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