Prothymosin alpha mRNA is expressed in competent and proliferating rat thyroid cells (FRTL-5) but is not sufficient to elicit cell progression through the cell cycle.
Using flow cytometry we observed the effects that different hormonal treatments had on the progression of rat thyroid (FRTL-5) cells through the cell cycle. The absence of hormones or the addition of TSH (6 mU/ml) did not induce DNA synthesis; however, the addition of IGF-I (30 ng/ml) promoted cell proliferation. The number of cells recruited by IGF-I was lower than when IGF-I and TSH were used. We therefore concluded that we had a model with three different types of cells: (1) quiescent cells, cells cultured in the absence of hormones, considered to be G0-arrested cells, (2) competent cells, TSH-treated cells that did not proliferate (being arrested in a cycle phase different from G0) and (3) actively proliferating cells, cells treated with TSH plus IGF-I. Prothymosin alpha (PTA) mRNA levels were almost undetectable in cells cultured without hormones at all times studied, i.e. 8, 14 and 24 h. On the contrary, TSH and/or IGF-I greatly increased PTA mRNA. These data indicate that G0-arrested quiescent cells do not express PTA mRNA and that PTA mRNA is induced when FRTL-5 cells are committed to proliferate by the addition of TSH, in spite of being arrested by the lack of IGF-I. We therefore conclude that PTA mRNA expression may be an event that is necessary for cells to proliferate, but that it is not sufficient for the promotion of cell progression through the cell cycle.
Alvarez
C V
CV
Departamento de Fisiologia, Laboratorio de Neurociencias Ramon Dominguez, Santiago de Compostela, Spain.
Zalvide
J B
JB
Cancio
E
E
Dieguez
C
C
Regueiro
B J
BJ
Vega
F V
FV
Dominguez
F
F
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D002460:Cell Line; D015870:Gene Expression / Q000187:drug effects; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D011498:Protein Precursors / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D016192:Resting Phase, Cell Cycle / Q000235:genetics / Q000502:physiology; D013947:Thymosin / Q000031:analogs & derivatives* / Q000235:genetics; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology
D011498:Protein Precursors; D012333:RNA, Messenger; C040782:prothymosin alpha; D013947:Thymosin; D007334:Insulin-Like Growth Factor I; D013972:Thyrotropin