RESUMEN
BACKGROUND: The molecular chaperone heat shock protein-90 (Hsp90) is a promising cancer drug target, but current Hsp90-based therapy has so far shown limited activity in the clinic. METHODS: We tested the efficacy of a novel mitochondrial-targeted, small-molecule Hsp90 inhibitor, Gamitrinib (GA mitochondrial matrix inhibitor), in the Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) model. The TRAMP mice receiving 3-week or 5-week systemic treatment with Gamitrinib were evaluated for localised or metastatic prostate cancer, prostatic intraepithelial neoplasia (PIN) or localised inflammation using magnetic resonance imaging, histology and immunohistochemistry. Treatment safety was assessed histologically in organs collected at the end of treatment. The effect of Gamitrinib on mitochondrial dysfunction was studied in RM1 cells isolated from TRAMP tumours. RESULTS: Systemic administration of Gamitrinib to TRAMP mice inhibited the formation of localised prostate tumours of neuroendocrine or adenocarcinoma origin, as well as metastatic prostate cancer to abdominal lymph nodes and liver. The Gamitrinib treatment had no effect on PIN or prostatic inflammation, and caused no significant animal weight loss or organ toxicity. Mechanistically, Gamitrinib triggered acute mitochondrial dysfunction in RM1 cells, with loss of organelle inner membrane potential and release of cytochrome-c in the cytosol. CONCLUSIONS: The Gamitrinib has pre-clinical activity and favourable tolerability in a genetic model of localised and metastatic prostate cancer in immunocompetent mice. Selective targeting of mitochondrial Hsp90 could provide novel molecular therapy for patients with advanced prostate cancer.
Asunto(s)
Adenocarcinoma/prevención & control , Antineoplásicos/uso terapéutico , Proliferación Celular/efectos de los fármacos , Guanidinas/uso terapéutico , Proteínas HSP90 de Choque Térmico/antagonistas & inhibidores , Lactamas Macrocíclicas/uso terapéutico , Neoplasias de la Próstata/prevención & control , Adenocarcinoma/genética , Adenocarcinoma/patología , Animales , Antineoplásicos/farmacología , Células Cultivadas , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Evaluación Preclínica de Medicamentos , Femenino , Predisposición Genética a la Enfermedad , Guanidinas/farmacología , Proteínas HSP90 de Choque Térmico/metabolismo , Lactamas Macrocíclicas/farmacología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Mitocondrias/efectos de los fármacos , Mitocondrias/metabolismo , Terapia Molecular Dirigida/métodos , Metástasis de la Neoplasia , Neoplasia Intraepitelial Prostática/genética , Neoplasia Intraepitelial Prostática/patología , Neoplasia Intraepitelial Prostática/prevención & control , Neoplasias de la Próstata/genética , Neoplasias de la Próstata/patologíaRESUMEN
Contributing to bone-specific expression of the osteocalcin gene is the promoter element OC Box I (-99 to -76), which binds both Hox proteins and another nonhomeodomain factor (designated OCBP for osteocalcin-box binding protein) (Hoffmann et al. [1996] J Cell Biochem 61:310-324). OCBP correlates with increased promoter activity and may, therefore, be important to development or maintenance of the osteoblast phenotype. To identify OCBP candidates, we used a multimerized OC Box I sequence to screen a gammagt11 cDNA expression library, constructed from the rat osteosarcoma osteoblastic ROS 17/2.8 cell line, for cDNA clones encoding factors that recognize this element. Mutant OC Box I sequences that do not bind OCBP and/or homeodomain proteins were used to counterscreen the cDNA isolates. Clones showing binding specificity were sequenced and further characterized for patterns of expression in different tissues and cell lines. Among the characterized nonhomeodomain-related isolates, we identified a nucleolin, a clone encoding rCAP2 that is related to myogenic differentiation and more importantly, a cDNA clone containing a previously uncharacterized gene that has been designated as a cell differentiation-related factor (DRF). DRF mRNA is highly expressed in ROS 17/2.8 cells and in a developmentally regulated pattern during osteoblast differentiation, being upregulated at the postproliferative maturation transition and coinciding with the induction of osteocalcin gene expression. The 7.7-kb transcript encoded by clone 44 is abundantly expressed in osteoblasts, but the mRNA was not present at detectable levels in bone and soft tissues by Northern blot analysis. However, related expressed sequence tags were recently reported in cDNA libraries of rat lung and mouse sympathetic ganglion. The identification of DRF represents a novel osteoblast differentiation-specific marker related to osteocalcin expression. The identification of DRF may further facilitate definition of gene regulatory mechanisms mediating the final stages of bone cell differentiation
Asunto(s)
Proteínas Nucleares/genética , Osteoblastos/citología , Osteocalcina/genética , Regiones Promotoras Genéticas , Animales , Secuencia de Bases , Diferenciación Celular , División Celular , ADN Complementario , Datos de Secuencia Molecular , Proteínas Nucleares/metabolismo , Osteoblastos/metabolismo , Osteocalcina/metabolismo , Fenotipo , Unión Proteica , Ratas , Secuencias Reguladoras de Ácidos Nucleicos , Transcripción Genética , Células Tumorales CultivadasRESUMEN
Multiple regulatory elements and intricate protein-DNA interactions mediate the transcription of the human histone H4 genes in a cell growth-dependent manner. Upon analysis of the regulatory elements of the FO108 histone H4 gene, we identified several potential YY1 binding sites. In this study, we have analyzed the ability of the transcription factor YY1 to interact at these sites in vitro by using electrophoretic mobility shift assays in combination with oligonucleotide competition and antibody immunoreactivity. We show that YY1 specifically binds transcriptional regulatory elements at -340 nt (site III), -100 nt (site I) and at least two domains within the coding region of the histone H4 gene. To test if these elements were functionally responsive to YY1, we performed transient expression experiments in Drosophila S-2 cells transfected with heterologous reporter gene constructs driven by histone H4 gene segments fused to the thymidine kinase promoter. Co-expression of YY1 stimulated promoter activity of these constructs relative to the reporter construct lacking histone H4 gene fragments. Our results suggest that YY1 contributes to transcriptional regulation of the histone H4 gene through interactions at multiple regulatory elements.
Asunto(s)
Proteínas de Unión al ADN/genética , Histonas/genética , Secuencias Reguladoras de Ácidos Nucleicos/genética , Factores de Transcripción/genética , Animales , Sitios de Unión , Línea Celular , Proteínas de Unión al ADN/metabolismo , Drosophila , Factores de Unión al ADN Específico de las Células Eritroides , Regulación de la Expresión Génica , Genes Reporteros/genética , Humanos , Oligodesoxirribonucleótidos/genética , Regiones Promotoras Genéticas/genética , Factores de Transcripción/metabolismo , Transfección , Factor de Transcripción YY1RESUMEN
The multifunctional transcription factor YY1 is associated with the nuclear matrix. In osteoblasts, the interaction of several nuclear matrix-associated transcription factors with the bone specific osteocalcin gene contributes to tissue-specific and steroid hormone-mediated transcription. A canonical nuclear matrix targeting signal (NMTS) is present in all members of the AML/CBFbeta transcription factor family, but not in other transcription factors. Therefore, we defined sequences that direct YY1 (414 amino acids) to the nuclear matrix. A series of epitope tagged deletion constructs were expressed in HeLa S3 and in human Saos-2 osteosarcoma cells. Subcellular distribution was determined in whole cells and nuclear matrices in situ by immunofluorescence. We demonstrated that amino acids 257-341 in the C-terminal domain of YY1 are necessary for nuclear matrix association. We also observed that sequences within the N-terminal domain of YY1 permit weak nuclear matrix binding. Our data further suggest that the Gal4 epitope tag contains sequences that affect subcellular localization, but not targeting to the nuclear matrix. The targeted association of YY1 with the nuclear matrix provides an additional level of functional regulation for this transcription factor that can exhibit positive and negative control.
Asunto(s)
Nucléolo Celular/metabolismo , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/metabolismo , Matriz Nuclear/metabolismo , Factores de Transcripción/química , Factores de Transcripción/metabolismo , Transcripción Genética , Animales , Compartimento Celular , Línea Celular , Proteínas de Unión al ADN/genética , Factores de Unión al ADN Específico de las Células Eritroides , Técnica del Anticuerpo Fluorescente , Células HeLa , Humanos , Ratones , Oligonucleótidos/genética , Plásmidos/genética , Eliminación de Secuencia , Relación Estructura-Actividad , Factores de Transcripción/genética , Activación Transcripcional , Transfección , Factor de Transcripción YY1RESUMEN
Proteins of the ATF/CREB class of transcription factors stimulate gene expression of several cell growth-related genes through protein kinase A-related cAMP response elements. The promoter activity of cell cycle regulated histone H4 genes is regulated by at least four principal cis-acting elements which mediate G1/S phase control and/or enhancement of transcription during the cell cycle. Using protein-DNA interaction assays we show that the H4 promoter contains two ATF/CREB recognition motifs which interact with CREB, ATF1, and ATF2 but not with ATF4/CREB2. One ATF/CRE motif is located in the distal promoter at the nuclear matrix-associated Site IV, and the second motif is present in the proximal promoter at Site I. Both ATF/CRE motifs overlap binding sequences for the multifunctional YY1 transcription factor, which has previously been shown to be nuclear matrix associated. Subnuclear fractionation reveals that there are two ATF1 isoforms which appear to differ with respect to DNA binding activity and partition selectively between nuclear matrix and nonmatrix compartments, consistent with the role of the nuclear matrix in regulating gene expression. Site-directed mutational studies demonstrate that Site I and Site IV together support ATF1- and CREB-induced trans-activation of the H4 promoter. Thus, our data establish that ATF/CREB factors functionally modulate histone H4 gene transcription at distal and proximal promoter elements.
Asunto(s)
Ciclo Celular/fisiología , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/metabolismo , Regulación de la Expresión Génica , Histonas/biosíntesis , Histonas/genética , Matriz Nuclear/metabolismo , Regiones Promotoras Genéticas , Factores de Transcripción/metabolismo , Activación Transcripcional , Factor de Transcripción Activador 1 , Factor de Transcripción Activador 2 , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Sitios de Unión , Células COS , Secuencia de Consenso , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/química , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Proteínas de Unión al ADN/química , Proteínas de Unión al ADN/metabolismo , Factores de Unión al ADN Específico de las Células Eritroides , Fase G1 , Células HeLa , Humanos , Leucina Zippers , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Oligodesoxirribonucleótidos , Proteínas Recombinantes/metabolismo , Reticulocitos/metabolismo , Fase S , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Factores de Transcripción/química , Transfección , Factor de Transcripción YY1 , Dedos de ZincRESUMEN
The subnuclear location of transcription factors may functionally contribute to the regulation of gene expression. Several classes of gene regulators associate with the nuclear matrix in a cell type, cell growth, or cell cycle related-manner. To understand control of nuclear matrix-transcription factor interactions during tissue development, we systematically analyzed the subnuclear partitioning of a panel of transcription factors (including NMP-1/YY-1, NMP-2/AML, AP-1, and SP-1) during osteoblast differentiation using biochemical fractionation and gel shift analyses. We show that nuclear matrix association of the tissue-specific AML transcription factor NMP-2, but not the ubiquitous transcription factor YY1, is developmentally upregulated during osteoblast differentiation. Moreover, we show that there are multiple AML isoforms in mature osteoblasts, consistent with the multiplicity of AML factors that are derived from different genes and alternatively spliced cDNAs. These AML isoforms include proteins derived from the AML-3 gene and partition between distinct subcellular compartments. We conclude that the selective partitioning of the YY1 and AML transcription factors with the nuclear matrix involves a discriminatory mechanism that targets different classes and specific isoforms of gene regulatory factors to the nuclear matrix at distinct developmental stages. Our results are consistent with a role for the nuclear matrix in regulating the expression of bone-tissue specific genes during development of the mature osteocytic phenotype.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Regulación del Desarrollo de la Expresión Génica , Proteínas de Neoplasias , Matriz Nuclear/metabolismo , Proteínas Nucleares/metabolismo , Osteoblastos/citología , Proteínas Proto-Oncogénicas , Factores de Transcripción/metabolismo , Animales , Antígenos Nucleares , Compartimento Celular , Subunidad alfa 2 del Factor de Unión al Sitio Principal , Factores de Unión al Sitio Principal , Factores de Unión al ADN Específico de las Células Eritroides , Osteoblastos/metabolismo , Ratas , Factor de Transcripción Sp1/metabolismo , Factor de Transcripción AP-1/metabolismo , Factor de Transcripción YY1RESUMEN
Fetal rat calvarial-derived osteoblasts in vitro (ROB) reinitiate a developmental program from growth to differentiation concomitant with production of a bone tissue-like organized extracellular matrix. To identify novel genes which may mediate this sequence, we isolated total RNA from three stages of the cellular differentiation process (proliferation, extracellular matrix maturation, and mineralization), for screening gene expression by the differential mRNA display technique. Of 15 differentially displayed bands that were analyzed by Northern blot analysis, one prominent 310 nucleotide band was confirmed to be proliferation-stage specific. Northern blot analysis showed a 600-650 nt transcript which was highly expressed in proliferating cells and decreased to trace levels after confluency and throughout the differentiation process. We have designated this transcript PROM-1 (for proliferating cell marker). A full length PROM-1 cDNA of 607 bp was obtained by 5' RACE. A short open reading frame encoded a putative 37 amino acid peptide with no significant similarity to known sequences. Expression of PROM-1 in the ROS 17/2.8 osteosarcoma cell line was several fold greater than in normal diploid cells and was not downregulated when ROS 17/2.8 cells reached confluency. The relationship of PROM-1 expression to cell growth was also observed in diploid fetal rat lung fibroblasts. Hydroxyurea treatment of proliferating osteoblasts blocked PROM-1 expression; however, its expression was not cell cycle regulated. Upregulation of PROM-1 in response to TGF-beta paralleled the stimulatory effects on growth as quantitated by histone gene expression. In conclusion, PROM-1 represents a small cytoplasmic polyA containing RNA whose expression is restricted to the exponential growth period of normal diploid cells; the gene appears to be deregulated in tumor derived cell lines.
Asunto(s)
Biomarcadores , Técnicas Genéticas , Osteoblastos/citología , Proteínas/genética , ARN Mensajero/análisis , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Northern Blotting , Calcitriol/farmacología , Diferenciación Celular/genética , División Celular/genética , Células Cultivadas , Cartilla de ADN , ADN Complementario , Diploidia , Regulación del Desarrollo de la Expresión Génica , Regulación Neoplásica de la Expresión Génica , Hidroxiurea/farmacología , Pulmón/citología , Pulmón/embriología , Datos de Secuencia Molecular , Osteoblastos/efectos de los fármacos , Osteosarcoma/tratamiento farmacológico , Osteosarcoma/genética , Osteosarcoma/patología , Reacción en Cadena de la Polimerasa/métodos , ARN Mensajero/genética , Ratas , Análisis de Secuencia de ADN , Cráneo/citología , Cráneo/embriología , Transcripción Genética , Factor de Crecimiento Transformador beta/farmacología , Células Tumorales CultivadasRESUMEN
The responsiveness of genes to steroid hormones is principally mediated by functional interactions between DNA-bound hormone receptors and components of the transcriptional initiation machinery, including TATA-binding protein, TFIIB, or other RNA polymerase II associated factors. This interaction can be physiologically modulated by promoter context-specific transcription factors to facilitate optimal responsiveness of gene expression to hormone stimulation. One postulated regulatory mechanism involves the functional antagonism between hormone receptors and nonreceptor transcription factors interacting at the same hormone response element. Here we demonstrate that the multifunctional regulator YY1 represses 1,25-dihydroxyvitamin D3 (vitamin D)-induced transactivation of the bone tissue-specific osteocalcin gene. We identify YY1 recognition sequences within the vitamin D response element (VDRE) of the osteocalcin gene that are critical for YY1-dependent repression of vitamin D-enhanced promoter activity. We show that YY1 and vitamin D receptor (VDR)/retinoid X receptor heterodimers compete for binding at the osteocalcin VDRE. In addition, we find that YY1 interacts directly with TFIIB, and that one of the two tandemly repeated polypeptide regions of TFIIB spanning the basic domain is responsible for this interaction. TFIIB and VDR can also interact directly, and these factors synergize to mediate transactivation. Our results suggest that YY1 regulates vitamin D enhancement of osteocalcin gene transcription in vivo by interfering with the interactions of the VDR with both the VDRE and TFIIB.
Asunto(s)
Huesos/metabolismo , Proteínas de Unión al ADN/metabolismo , Osteocalcina/genética , Receptores de Calcitriol/metabolismo , Receptores de Ácido Retinoico/metabolismo , Factores de Transcripción/metabolismo , Activación Transcripcional , Vitamina D/farmacología , Animales , Sitios de Unión , Unión Competitiva , Huesos/efectos de los fármacos , Factores de Unión al ADN Específico de las Células Eritroides , Modelos Genéticos , Proteínas Nucleares/metabolismo , Osteocalcina/biosíntesis , Osteosarcoma , Ratas , Proteínas Recombinantes/metabolismo , Receptores X Retinoide , Factor de Transcripción TFIIB , Transfección , Células Tumorales Cultivadas , Factor de Transcripción YY1RESUMEN
Tissue and cell-type specific expression of the rat osteocalcin (rOC) gene involves the interplay of multiple transcriptional regulatory factors. In this report we demonstrate that AML-1 (acute myeloid leukemia-1), a DNA-binding protein whose genes are disrupted by chromosomal translocations in several human leukemias, interacts with a sequence essential for enhancing tissue-restricted expression of the rOC gene. Deletion analysis of rOC promoter-chloramphenicol acetyltransferase constructs demonstrates that an AML-1-binding sequence within the proximal promoter (-138 to -130 nt) contributes to 75% of the level of osteocalcin gene expression. The activation potential of the AML-1-binding sequence has been established by overexpressing AML-1 in osteoblastic as well as in nonosseous cell lines. Overexpression not only enhances rOC promoter activity in osteoblasts but also mediates OC promoter activity in a nonosseous human fibroblastic cell line. A probe containing this site forms a sequence specific protein-DNA complex with nuclear extracts from osteoblastic cells but not from nonosseous cells. Antisera supershift experiments indicate the presence of AML-1 and its partner protein core-binding factor beta in this osteoblast-restricted complex. Mutations of the critical AML-1-binding nucleotides abrogate formation of the complex and strongly diminish promoter activity. These results indicate that an AML-1 related protein is functional in cells of the osteoblastic lineage and that the AML-1-binding site is a regulatory element important for osteoblast-specific transcriptional activation of the rOC gene.
Asunto(s)
Proteínas de Unión al ADN , ADN/genética , ADN/metabolismo , Proteínas de Neoplasias/genética , Proteínas de Neoplasias/metabolismo , Osteocalcina/genética , Proteínas Proto-Oncogénicas , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Animales , Secuencia de Bases , Sitios de Unión/genética , Línea Celular , Secuencia de Consenso , Subunidad alfa 2 del Factor de Unión al Sitio Principal , ADN Complementario/genética , Humanos , Datos de Secuencia Molecular , Osteoblastos/metabolismo , Regiones Promotoras Genéticas , Ratas , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Activación TranscripcionalRESUMEN
NMP-1 was initially identified as a nuclear matrix-associated DNA-binding factor that exhibits sequence-specific recognition for the site IV regulatory element of a histone H4 gene. This distal promoter domain is a nuclear matrix interaction site. In the present study, we show that NMP-1 is the multifunctional transcription factor YY1. Gel-shift and Western blot analyses demonstrate that NMP-1 is immunoreactive with YY1 antibody. Furthermore, purified YY1 protein specifically recognizes site IV and reconstitutes the NMP-1 complex. Western blot and gel-shift analyses indicate that YY1 is present within the nuclear matrix. In situ immunofluorescence studies show that a significant fraction of YY1 is localized in the nuclear matrix, principally but not exclusively associated with residual nucleoli. Our results confirm that NMP-1/YY1 is a ubiquitous protein that is present in both human cells and in rat osteosarcoma ROS 17/2.8 cells. The finding that NMP-1 is identical to YY1 suggests that this transcriptional regulator may mediate gene-matrix interactions. Our results are consistent with the concept that the nuclear matrix may functionally compartmentalize the eukaryotic nucleus to support regulation of gene expression.
Asunto(s)
Núcleo Celular/química , Proteínas de Unión al ADN/aislamiento & purificación , Factores de Transcripción/aislamiento & purificación , Animales , Especificidad de Anticuerpos , Secuencia de Bases , Sitios de Unión , Western Blotting , Compartimento Celular , Nucléolo Celular/química , Nucléolo Celular/ultraestructura , Núcleo Celular/ultraestructura , Reacciones Cruzadas , ADN/metabolismo , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/inmunología , Proteínas de Unión al ADN/metabolismo , Factores de Unión al ADN Específico de las Células Eritroides , Células HeLa , Humanos , Datos de Secuencia Molecular , Matriz Nuclear/química , Oligodesoxirribonucleótidos/metabolismo , Unión Proteica , Ratas , Proteínas Recombinantes/aislamiento & purificación , Proteínas Recombinantes/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/inmunología , Factores de Transcripción/metabolismo , Factor de Transcripción YY1RESUMEN
Osteoblasts derived from Day 21 fetal rat calvaria grown on films of collagen type I exhibit an earlier and enhanced expression of the differentiated phenotype, compared to cells cultured on plastic. The temporal expression of genes characterizing three distinct periods of growth and differentiation are dramatically modified. During the initial proliferation period, expression of genes normally expressed at high levels on plastic (fibronectin, beta 1 integrin, and actin) was decreased from 50 to 70% in cells grown on collagen. Genes normally expressed at maximal levels in the postproliferative period (osteonectin, osteocalcin, and osteopontin) were up-regulated severalfold very early. Alkaline phosphatase enzyme activity was elevated 2- to 3-fold during the proliferation period, while mRNA levels remained low, suggesting post-transcriptional modifications. The most dramatic consequence of culture of cells on collagen is the accelerated and uniform mineralization of the matrix in contrast to the focal mineralization confined to bone nodules in cultures on plastic. Type I collagen supports maintenance of osteoblast phenotypic properties of passaged cells in the absence of glucocorticoid supplementation required for differentiation of osteoblasts subcultivated on plastic. Treatment of proliferating rat osteoblasts on plastic with 1,25(OH)2D3 blocks osteoblast differentiation and matrix mineralization. Although differentiation-related genes (alkaline phosphatase and osteocalcin) were up-regulated by vitamin D, culture on the collagen matrix could not overcome the inhibition of mineralization. Taken together, these studies define the critical role of type I collagen in mediating the signaling cascade for expression of a mature osteoblast phenotype and mineralization of the extracellular matrix in a physiological manner.
Asunto(s)
Colágeno/fisiología , Proteínas de la Matriz Extracelular/biosíntesis , Regulación del Desarrollo de la Expresión Génica , Osteoblastos/fisiología , Fosfatasa Alcalina/metabolismo , Animales , Biomarcadores , Calcificación Fisiológica/fisiología , Proteínas de Unión al Calcio/biosíntesis , Proteínas de Unión al Calcio/genética , Adhesión Celular/efectos de los fármacos , Diferenciación Celular/efectos de los fármacos , División Celular/efectos de los fármacos , Células Cultivadas , Colecalciferol/farmacología , Desarrollo Embrionario y Fetal , Proteínas de la Matriz Extracelular/genética , Osteoblastos/citología , Osteoblastos/enzimología , Osteopontina , Fenotipo , Plásticos , ARN Mensajero/biosíntesis , Ratas , Sialoglicoproteínas/biosíntesis , Sialoglicoproteínas/genética , Cráneo , Regulación hacia ArribaRESUMEN
We have recently demonstrated that the iv administration of 0.6-60 micrograms/kg.day of acidic fibroblast growth factor (acidic FGF) increases thyroid weight in male and female rats. Interestingly, measurement of serum TSH and thyroid hormones in rats treated with 6 micrograms/kg.day acidic FGF for 30 days revealed only a slight increase in serum T4 and reverse T3 concentrations. Since thyroid function was only examined 24 h after the 30th daily treatment, we performed a series of experiments to evaluate the effects of acidic FGF on thyroid function following single and 6 multiple injections of acidic FGF. There was a small increase in the serum TSH concentrations at 2, 4, 8, and 24 h after a single high dose iv injection of acidic FGF (60 micrograms/kg). In contrast, serum T3 concentrations were slightly decreased at 2, 4, and 8 h after acidic FGF administration. There was no effect of a single injection of acidic FGF on serum T4, reverse T3, or thyroglobulin concentrations. After 6 days of treatment, there was a 34% increase in the thyroid weights of rats treated with acidic FGF. Analysis of serum hormones revealed a slight increase in serum TSH, T3, and T4 concentrations in acidic FGF-treated rats, but no change in serum reverse T3 or thyroglobulin concentrations. There was no effect of acidic FGF administration on thyroid radioiodine uptake, the intrathyroidal metabolism of radioiodine, or the relative amounts of thyroidal thyroglobulin or peroxidase messenger RNAs, or on liver 5'-deiodinase activity. In hypophysectomized rats, with no detectable levels of serum TSH, acidic FGF failed to increase thyroid weight. These data suggest that FGFs may participate with TSH in the regulation of thyroid weight and colloid accumulation, and that autocrine or paracrine growth factors may be involved in the pathogenesis of colloid goiter.