Invasion Of Thyroid Cancer Cells Research Articles

The regulation of proliferation and invasion in differentiated thyroid cancer by growth factors.

Invasion and metastasis are the primary cause of death in patients with follicular thyroid cancer (FTC). The thyroid is a micro-economic system in which proliferation and differentiation was supposed to be under the major control of only a single hormone (thyroid stimulating hormone-TSH). It has shown, however, that a complex network of various growth factors regulates growth and invasion of thyroid cancer cells. A growing literature has established the close association between malignant tumor progression and growth regulatory aberrations in cancer cells. Most of these studies have focused on the phenomenon, that advanced and more aggressive tumors or metastases lost the sensitivity to growth inhibitors, such as transforming growth factor beta. These findings highlight two aberrations of growth regulation which may favour progression of malignant disease and acquisition of metastatic competence: (1) Resistance to growth factor inhibitors and (2) growth autonomy of metastatic follicular thyroid cancer cells.

The Cytoplasmic Domain of proEGF Negatively Regulates Motility and Elastinolytic Activity in Thyroid Carcinoma Cells

The intracellular domains of the membrane-anchoring regions of some precursors of epidermal growth factor (EGF) family members have intrinsic biologic activities. We have determined the role of the human proEGF cytoplasmic domain (proEGFcyt) as part of the proEGF transmembrane-anchored region (proEGFctF) in the regulation of motility and elastinolytic invasion in human thyroid cancer cells. We found proEGFctF to act as a negative regulator of motility and elastin matrix penetration and the presence of proEGFcyt or proEGF22.23 resulted in a similar reduction in motility and elastinolytic migration. This activity was counteracted by EGF-induced activation of EGF receptor signaling. Decreased elastinolytic migratory activity in the presence of proEGFctF and proEGFcyt/proEGF22.23 coincided with decreased secretion of elastinolytic procathepsin L. The presence of proEGFctF and proEGFcyt/proEGF22.23 coincided with the specific transcriptional up-regulation of t-SNARE member SNAP25. Treatment with siRNA-SNAP25 resulted in motility and elastin migration being restored to normal levels. Epidermal growth factor treatment down-regulated SNAP25 protein by activating EGF receptor-mediated proteasomal degradation of SNAP25. These data provide first evidence for an important function of the cytoplasmic domain of the human proEGF transmembrane region as a novel suppressor of motility and cathepsin L-mediated elastinolytic invasion in human thyroid carcinoma cells and suggest important clinical implications for EGF-expressing tumors.

Potent Inhibition of Thyroid Cancer Cells by the MEK Inhibitor PD0325901 and Its Potentiation by Suppression of the PI3K and NF-κB Pathways

We recently demonstrated inhibition of thyroid cancer cells by the MEK inhibitor CI-1040. The objective of this study was to use a potent new-generation MEK inhibitor PD0325901 to further investigate the therapeutic potential of specifically targeting MEK in the MAP kinase pathway for thyroid cancer. We examined the effects of PD0325901 on a variety of cellular and molecular activities of thyroid cancer cell lines with distinct genotypes. PD0325901 remarkably inhibited MAP kinase pathway signaling in the thyroid cancer cells tested. It potently inhibited cell proliferation (IC(50) = 0.059-0.783 microM) and arrested cell cycle at the G0/G1 phase of cells harboring BRAF or RAS mutations but not cells harboring wild-type alleles or the RET/PTC1 rearrangement. Synergistic inhibitory effects were observed when PD0325901 was combined with phosphatidylinositol 3-kinase (PI3K) or NF-kappaB pathway inhibitors in most cells, including the RET/PTC1-harboring cells. PD0325901 could inhibit invasion and anchorage-independent growth of thyroid cancer cells independently of the type of genetic alterations. This compound did not seem to have significant proapoptotic effects, however. The MEK inhibitor PD0325901 has a wide range of potent inhibitory effects on thyroid cancer cells, some of which seemed to be genotype-selective, consistent with the results previously observed with an early-generation MEK inhibitor, CI-1040. The data provide further evidence that targeted inhibition of MEK may be therapeutically effective for thyroid cancer, particularly if the PI3K and NF-kappaB pathways are concurrently inhibited.

Activating Transcription Factor-1-mediated Hepatocyte Growth Factor-induced Down-regulation of Thrombospondin-1 Expression Leads to Thyroid Cancer Cell Invasion

Hepatocyte growth factor (HGF) plays a major role in the pathogenesis of a variety of human epithelial tumors including papillary carcinoma of the thyroid. Previous reports demonstrated that HGF, acting through the Met receptor, repressed thrombospondin-1 (TSP-1) expression. To study the mechanisms by which HGF down-regulated TSP-1 expression, we transiently transfected a panel of deleted human TSP-1 promoter reporter plasmids into papillary thyroid carcinoma cells. We identified a region between -1210 and -1123 bp relative to the transcription start site that is responsive to HGF treatment and harbors a cAMP-responsive element (CRE) at position -1199 (TGACGTCC). Overexpression of various members of the CRE-binding protein family identified activating transcription factor-1 (ATF-1) as the transcription factor responsible for HGF-induced repression of TSP-1 promoter activity. This inhibition was associated with a concomitant increase in the abundance of nuclear ATF-1 protein. Gel shift and antibody supershift studies indicated that ATF-1 was involved in DNA binding to the TSP-1-CRE site. Finally, we utilized small hairpin RNA to target ATF-1 and showed that these small interfering RNA constructs significantly inhibited ATF-1 expression at both the RNA and the protein level. ATF-1 knockdown prevented HGF-induced down-regulation of TSP-1 promoter activity and protein expression and also reduced HGF-dependent tumor cell invasion. Taken together, our results indicate that HGF-induced down-regulation of TSP-1 expression is mediated by the interaction of ATF-1 with the CRE binding site in the TSP-1 promoter and that this transcription factor plays a crucial role for tumor invasiveness in papillary carcinoma of the thyroid triggered by HGF.

Differentiated thyroid cancer cell invasion is regulated through epidermal growth factor receptor-dependent activation of matrix metalloproteinase (MMP)-2/gelatinase A

Mechanisms of invasion in thyroid cancer remain poorly understood. We hypothesized that signaling via the epidermal growth factor receptor (EGFR) stimulates thyroid cancer cell invasion by altering the expression and cleavage of matrix metalloproteinases (MMPs). Papillary and follicular carcinoma cell lines were treated with EGF, the EGFR tyrosine kinase inhibitor AG1478, and the MMP inhibitors GM-6001 and Col-3. Flow cytometry was used to detect EGFR. In vitro invasion assays, gelatin zymography, and quantitative reverse transcription-PCR were used to assess the changes in invasive behavior and MMP expression and activation. All cell lines were found to overexpress functional EGFR. EGF stimulated invasion by thyroid cancer cells up to sevenfold (P<0.0001), a process that was antagonized completely by AG1478 and Col-3, partially by GM-6001, but not by the serine protease inhibitor aprotinin. EGF upregulated expression of MMP-9 (2.64- to 8.89-fold, P<0.0001) and membrane type-1 MMP (MT1-MMP, 1.97- to 2.67-fold, P<0.0001). This effect was blocked completely by AG1478 and partially by Col-3. The activation of MMP-2 paralleled MT1-MMP expression. We demonstrate that MMPs are critical effectors of invasion in the papillary and follicular thyroid cancer cell lines studied. Invasion is regulated by signaling through EGFR, an effect mediated by augmentation of gelatinase expression and activation. MMP inhibitors and growth factor antagonists may be effective tumoristatic agents for the treatment of aggressive thyroid carcinomas.

BRAFV600EPromotes Invasiveness of Thyroid Cancer Cells through Nuclear Factor κB Activation

The BRAFV600E mutation is closely linked to tumorigenesis and malignant phenotype of papillary thyroid cancer. Signaling pathways activated by BRAFV600E are still unclear except a common activation pathway, MAPK cascade. To investigate the possible target of BRAFV600E, we developed two different cell culture models: 1) doxycycline-inducible BRAFV600E-expressing clonal line derived from human thyroid cancer WRO cells originally harboring wild-type BRAF; 2) WRO, KTC-3, and NPA cells infected with an adenovirus vector carrying BRAFV600E. BRAFV600E expression induced ERK phosphorylation and cyclin D1 expression in these cells. The BRAFV600E-overexpressing cells also showed an increase of nuclear factor kappaB (NF-kappaB) DNA-binding activity, resulting in up-regulation of antiapoptotic c-IAP-1, c-IAP-2, and X-linked inhibitor of apoptosis. Furthermore, BRAFV600E expression also induced the expression of matrix metalloproteinase and cell invasion into matrigel through NF-kappaB pathway. Increased invasive ability by BRAFV600E expression was significantly inhibited by a specific NF-kappaB inhibitor, racemic dehydroxymethylepoxyquinomicin. These data indicate that BRAFV600E activates not only MAPK but also NF-kappaB signaling pathway in human thyroid cancer cells, leading to an acquisition of apoptotic resistance and promotion of invasion. Inactivation of NF-kappaB may provide a new therapeutic modality for thyroid cancers with BRAFV600E.

Lovastatin suppresses invasiveness of anaplastic thyroid cancer cells by inhibiting Rho geranylgeranylation and RhoA/ROCK signaling

Lovastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, inhibits the conversion of mevalonate from HMG-CoA. Previously, we have reported that lovastatin treatment induced the occurrence of apoptosis and differentiation in ARO anaplastic thyroid cancer cells. Here, we demonstrated that lovastatin inhibited the ARO cell invasiveness and delineated the underlying molecular mechanism. Lovastatin significantly suppressed the EGF-induced cell adhesion, actin filament reorganization and transmigration. Lovastatin also reduced EGF-induced increases in the levels of phosphorylated p125(FAK) and paxillin. These inhibitory effects mediated by lovastatin can be prevented by pretreatment of the cells with mevalonate or geranylgeraniol (GGOH), but not farnesol (FOH). Accordingly, the consuming and depletion of geranylgeranyl pyrophosphate and consequent suppression of the protein geranylgeranylation, which is essential for activation of Rho GTPases, might account for the lovastatin-induced inhibition of cell motility and invasion. Western blot analysis showed that lovastatin inhibited membrane translocation of Rho (e.g. RhoA and Rac1) through decreasing post-translational geranylgeranyl modification of Rho. In addition, treatment of the cells with specific inhibitors against Rho (Clostridium botulinum C3 transferase) or ROCK (Y-27632) abolished the GGOH-mediated prevention of, and restored the lovastatin-induced decrease of cell invasion. Taken together, our results suggested that lovastatin suppressed EGF-induced ARO cell invasiveness through the reduction of Rho geranylgeranylation, which in turn suppressed the membrane translocation, and subsequent suppression of Rho/ROCK and FAK/paxillin signaling.

Bone sialoprotein, matrix metalloproteinase 2, and alpha(v)beta3 integrin in osteotropic cancer cell invasion.

Bone sialoprotein (BSP) interacts separately with both matrix metalloproteinase 2 (MMP-2) and integrin alpha(v)beta3 and is overexpressed in many metastatic tumors. Its role in tumor biology, however, remains unclear. We investigated whether BSP enhances cancer cell invasiveness by forming a trimolecular complex with MMP-2 and cell-surface integrin alpha(v)beta3. Invasiveness of breast, prostate, lung, and thyroid tumor cell lines was measured with a modified Boyden chamber assay. Binding and co-localization of BSP, MMP-2, and integrin alpha(v)beta3 were investigated with immunoprecipitation and in situ hybridization. All statistical tests were two-sided. Treatment with BSP increased invasiveness of many breast, prostate, lung, and thyroid cancer cells through Matrigel in a dose-dependent manner. BSP at 50 nM increased the invasiveness of SW-579 thyroid cancer cells (95.2 units, 95% confidence interval [CI] = 90.4 to 100 units) by approximately 10-fold compared with that of untreated control SW-579 cells (9.1 units, 95% CI = 5.7 to 12.5 units) (P<.001). Addition of an inactive mutated BSP, in which BSP's integrin-binding RGD tripeptide was altered, or addition of integrin alpha(v)beta3-blocking antibodies resulted in invasiveness equivalent to that of untreated cells. Inhibiting cellular MMP-2 activity with chemical inhibitors or a specific antibody also blocked BSP-enhanced invasiveness. Osteopontin and dentin matrix protein 1, proteins related to BSP that also bind integrin alpha(v)beta3 and form complexes with other MMPs (but not MMP-2), did not enhance invasiveness. Immunoprecipitation showed that a complex containing BSP, integrin alpha(v)beta3, and MMP-2 formed in vitro. Addition of BSP increased the amount of MMP-2 bound by cells in an integrin-dependent fashion. Co-expression of BSP, integrin alpha(v)beta3, and MMP-2 in papillary thyroid carcinoma cells was shown by in situ hybridization. Cancer cells appear to become more invasive when BSP forms a cell-surface trimolecular complex by linking MMP-2 to integrin alpha(v)beta3.

Effects of TSH on the Production of VEGF, Angiogenesis, Growth, Invasion and Metastasis in Thyroid Cancer Cells

Effects of TSH on the Production of VEGF, Angiogenesis, Growth, Invasion and Metastasis in Thyroid Cancer Cells

The role of growth factors in proliferation and invasion of thyroid cancer

A growing literature has established the close association between tumor progression and growth regulatory aberrations in cancer cells. Most studies have focused on the phenomenon, that advanced tumors or metastases have lost the sensitivity to growth inhibitors. Metastasis are the primary cause of death in patients with differentiated thyroid cancer. Proliferation and differentiation of the thyroid was supposed to be under the major control of only a single hormone (thyroid stimulating hormone). However, we and others have shown that a complex network of various growth factors regulates growth and invasion of thyroid cancer cells. Our findings highlight two aberrations of growth regulation which may favour progression of malignancy and acquisition of metastatic competence: i) resistence to growth factor inhibitors and ii) growth autonomy of metastatic thyroid cancer cells.

Somatostatin analog octreotide inhibits the growth of differentiated thyroid cancer cells in vitro, but not in vivo.

Somatostatin and its analogs are antiproliferative in a wide range of normal and neoplastic tissues. In this study we investigated the effect of octreotide (SMS 201-995) on the invasion and growth of three follicular thyroid cancer (FTC) cell lines from one patient in vitro and in vivo. FTC133 was established from the primary tumor, FTC236 from a cervical lymph node metastasis, and FTC238 from a lung metastasis. Invasion was the ability of tumor cells to penetrate 8-microns pore polycarbonate membranes coated with Matrigel. Invasion and proliferation were analyzed using the MTT assay. For in vivo experiments, athymic nude mice were sc inoculated with 500,000 calls of FTC133. The animals were treated twice daily with octreotide sc (100-300 micrograms/kg). RIA studies yielded dose-dependent high plasma levels of octreotide (3.43-6.5 ng/mL). Octreotide had a biphasic effect, enhancing growth at low concentrations (1-10 nmol/mL) and inhibiting it at high concentrations (100 nmol to 1 mumol/mL). Octreotide had also a dose-dependent biphasic effect on the invasion of FTC, inhibiting the invasion of all follicular thyroid cancer lines at high concentrations. However, it affected invasion less than growth. Octreotide (10 nmol/mL) stimulated the invasion of FTC133 by 13%, whereas stimulation was lower in both FTC metastases (FTC236, 6%; FTC238, 7%; P < 0.01). At higher concentrations (100 nmol to 1 mumol/mL), octreotide inhibited invasion of FTC133 by 17% (FTC236, 15%; FTC238, 17%; P < 0.01). During a 3-week treatment period, octreotide had no antiproliferative effect on the growth of FTC133 cells in nude mice. In conclusion, octreotide at low concentrations stimulates and at high concentrations inhibits the growth and invasion of follicular thyroid cancer cells in culture. However, it has no effect on the growth of FTC cells in animal experiments. Thus, the value of octreotide as an antitumoral agent in follicular thyroid cancer must be critically questioned.

Tamoxifen antagonizes proliferation and invasion of estrogen receptor-negative metastatic follicular thyroid cancer cells via protein kinase C.

Tamoxifen inhibits invasion and growth of estrogen-receptor negative follicular thyroid cancer (FTC) cells in vitro and in vivo. To study the mechanisms involved, we documented the effects of tamoxifen and staurosporine on three metastatic FTC-cell lines. TPA (10 ng/ml) enhanced invasion and growth of FTC by 15% (P < 0.02). Tamoxifen (1.5 micromol/l) inhibited invasion of FTC133 by 36% (FTC236 30%; FTC238 32%; P < 0.01). TPA reversed the tamoxifen-mediated inhibition of invasion by 35% in FTC133 and 30% in FTC238 (P < 0.02). Staurosporine (10 ng/ml) inhibited invasion and growth of all FTC. At 0.1-1 ng/ml it enhanced the inhibitory effects of tamoxifen, but did not further inhibit invasion or growth at higher concentrations. We conclude that the antiproliferative and antiinvasive effects of tamoxifen on follicular thyroid cancer cells are at least partly mediated by an inhibition of protein kinase C.

Epidermal growth factor (EGF)- and transforming growth factor alpha-stimulated invasion and growth of follicular thyroid cancer cells can be blocked by antagonism to the EGF receptor and tyrosine kinase in vitro

We have shown recently that epidermal growth factor (EGF) enhanced invasion and growth of differentiated thyroid cancer cells in vitro and in vivo. The present study analyzed the effects of transforming growth factor alpha (TGF-alpha) on invasion and growth of a follicular thyroid cancer cell line (FTC133) and whether blocking the EGF receptor by a monoclonal antibody (Mab528) or blocking the tyrosine kinase of the receptor by genistein abolished the EGF- and TFG-alpha-mediated effects. Growth and invasion (penetration of 8-microns pore polycarbonate membranes coated with Matrigel) were determined by the dimethylthiazol-diphenyltetrazolium bromide assay. Epidermal growth factor (10 ng/l) stimulated invasion of FTC133 by 42% and TGF-alpha (10 ng/l) stimulated invasion of FTC133 by 27% (p < 0.02). Both growth factors also enhanced growth by 62% (EGF) and 30% (TGF-alpha) (p < 0.003). Epidermal growth factor receptor antibodies (1 microgram/ml) abolished EGF-mediated stimulation of invasion and growth completely and that of TGF-alpha by 93%. At 100 ng/ml genistein reversed EGF and TGF-alpha stimulation, and at 1 microgram/ml it inhibited invasion (27%) and growth (40%) of unstimulated FTC133 (p < 0.02). We conclude that TGF-alpha stimulates invasion and growth of follicular thyroid cancer by binding to the EGF receptors, that EGF- and TGF-alpha-mediated effects can be blocked by antagonism to the EGF receptor and to tyrosine kinase, and that genistein not only neutralized EGF and TGF-alpha effects but also inhibited invasion and growth of unstimulated FTC133.(ABSTRACT TRUNCATED AT 250 WORDS)

Biphasic effects of thyrotropin on invasion and growth of papillary and follicular thyroid cancer in vitro.

The rationale for TSH suppression in the treatment of follicular thyroid cancer (FTC) and papillary thyroid cancer (PTC) is to inhibit tumor growth, prevent recurrent disease, and eventually prolong survival. We analyzed the effects of TSH on invasion and growth of 3 FTC cell lines from 1 patient (FTC133, primary; FTC236, lymph node; FTC238, lung metastasis) and 2 PTC cell lines (PTC-UC1, PTC-UC3). Cell growth and invasion through an 8-micron pore polycarbonate membrane coated with Matrigel were measured using the MTT assay. The dose-response to TSH was biphasic, stimulating invasion and growth of FTC and PTC at low concentrations (0.1-10 mU/mL), and inhibiting them at high concentrations (100 mU/mL). Interestingly, the metastatic FTC cell lines had higher basal invasion, but were less responsive to TSH than the primary tumor. TSH (1 mU/mL) stimulated invasion of FTC133 by 21%, FTC236 by 8%, and FTC238 by 8% (p < 0.01). At 100 mU/mL, TSH inhibited invasion of FTC133 by 21%, compared to 11% in FTC236 and 12% in FTC238. Also, TSH dose-dependently influenced proliferation of follicular thyroid cancer cells. At low concentrations it stimulated growth of FTC133 (20%) and inhibited it at high concentrations (23%; p < 0.01). Again, the amplitude of TSH effects was significantly smaller in the cell lines from metastatic tumors. TSH affected invasion and growth of PTC-UC1 and PTC-UC3 also biphasically. These results show that TSH may act as a mitogenic and antimitogenic growth factor for invasion and proliferation of well-differentiated thyroid cancer cells in vitro.

Tamoxifen inhibits growth, migration, and invasion of human follicular and papillary thyroid cancer cells in vitro and in vivo

Tamoxifen inhibits growth, migration, and invasion of human follicular and papillary thyroid cancer cells in vitro and in vivo

Tamoxifen inhibits growth, migration, and invasion of human follicular and papillary thyroid cancer cells in vitro and in vivo.

Prognosis of differentiated thyroid cancer is best in young women. It has been proposed that sex steroids protect premenopausal women from aggressive thyroid malignancies. Some thyroid tissues have estrogen receptors, and estrogen stimulates human thyroid cells. Tamoxifen is thought to exert its antiproliferative effects mainly by blocking estrogen stimulation. However, recently, mechanisms independent of estrogen interactions were found to be important for the favorable effect. We investigated the effect of tamoxifen on the growth, migration, and invasion in three follicular thyroid cancer cell lines (FTC133, primary; FTC236, lymph node; and FTC238, lung metastasis) from one patient and two papillary lines (PTC-UC1 and PTC-UC3). Growth was measured by dimethylthiazol-diphenyltetrazolium bromide assays, and migration was determined by the ability of cells to penetrate 8-microns pore membranes, which were covered by Matrigel for invasion assays. For in vivo experiments, we used xenografts of FTC133 in nude mice. Tamoxifen (1.5 mumol/L) inhibited the growth of all thyroid cancer cell lines (FTC133, 59%; FTC236, 42%; FTC238, 46%; P < 0.01). This effect was less pronounced in PTC-UC1 (25%) and PTC-UC3 (19%; P < 0.006) cell lines. Tamoxifen also inhibited migration and invasion of FTC more than PTC. Invasion of FTC133 was inhibited by 36% (P < 0.01), FTC236 by 30%, and FTC238 by 32%. Immunohistochemistry showed no estrogen receptors in any cell line. Also, estradiol had no significant effect on the growth, migration, or invasion of FTC or PTC. Tamoxifen treatment inhibited the growth of FTC133 xenografts in nude mice by 52% compared to that in placebo-treated controls (P < 0.002). In conclusion, tamoxifen inhibited the growth, migration, and invasion of differentiated thyroid cancer cells in vitro and in vivo. This was not reversed by estrogen. Tamoxifen acts independently of estrogen interactions and may be useful as an adjuvant treatment for some differentiated human thyroid malignancies.

Transforming growth factor-beta 1 is a negative regulator for differentiated thyroid cancer: studies of growth, migration, invasion, and adhesion of cultured follicular and papillary thyroid cancer cell lines.

Invasion and metastasis may be caused by the escape of tumor cells from the negative control of growth factors. We analyzed the effects of transforming growth factor-beta 1 (TGF beta 1) on growth, migration, invasion, and adhesion in three follicular thyroid cancer cell lines (FTC133, primary; FTC236, lymph node metastasis; FTC238, lung metastasis) from one patient and in a papillary line (PTC-UC3). Cell growth was measured by dimethylthiazol-diphenyltetrazolium bromide assays, and migration (basal or epidermal growth factor stimulated) was determined by the ability of cells to penetrate 8-microns pore membranes that were covered with Matrigel for invasion assays. Moreover, we studied tumor cell adhesion to collagen type IV, fibronectin, and laminin. TGF beta 1 inhibited growth in FTC (FTC133, by 31%; FTC236, 15%; FTC238, 17%; P < 0.008), but not in PTC. Migration was inhibited in all cell lines. TGF beta 1 inhibited epidermal growth factor-stimulated migration of FTC133 by 43% vs. 29% without epidermal growth factor (P < 0.03). TGF beta 1 also inhibited invasion (FTC133, 32%; FTC236, 18%; FTC238, 16%; PTC-UC3, 32%; P < 0.02). All cell lines adhered preferably to collagen type IV and fibronectin. TGF beta 1 enhanced adhesion. Again, these effects were less pronounced in the FTC metastases. In conclusion, TGF beta 1 inhibits the growth, migration, and invasion of thyroid cancer cells in vitro. It enhances adhesion to components of the extracellular matrix. Metastatic thyroid tumors may be less responsive to the negative regulation of TGF beta 1.

Thyrotropin Stimulates Invasion and Growth of Follicular Thyroid Cancer Cells via PKC- Rather Than PKA-Activation

The signal transduction of TSH in invasion and growth of FTC 133, a human follicular thyroid cancer cell line, was investigated. TSH (0.01 -1 mIU/ml) stimulated invasion of FTC 133 by 21% and growth by 20% of basal. Cyclic AMP-stimulators and inhibitors had no effect at any concentration. The PKC-agonist TPA enhanced invasion and growth by 15%, whereas stauroporine, a PKC-antagonist, inhibited them by 32% and 60%, respectively. The latter also reversed TSH stimulation. EGF enhanced invasion (42%) and growth of FTC 133 (25%). Stauroporine did not reverse EGF stimulation. The tyrosine kinase antagonist gemstein reversed EGF, but not TSH stimulation. Pertussis toxin inhibited invasion (18%) and growth (22%). Cholera toxin was less inhibitive. We demonstrated for the first time, that TSH stimulates invasion and growth of human thyroid cancer cells in vitro by PKC- rather than PKA-stimulation.