Giovanni Villone

Transfected insulin-like growth factor II modulates the mitogenic response of rat thyrocytes in culture.

Rat thyroid cells (FRTL5), transfected with the sequence coding for rat insulin-like growth factor II (IGF-II) presented mRNA specific for the transfected IGF-II in most of the clones obtained (Tr clones). Tr7 and Tr12 cells maintained their ability to respond to the mitogenic effect of thyrotropin (TSH), while either exogenous IGF-I or IGF-II or insulin failed to stimulate their proliferation. In the absence of exogenous mitogens the Tr7 and Tr12 clones vigorously incorporated [3H]thymidine into DNA. This activity was significantly inhibited by sm1.2, a monoclonal antibody against rat IGF-II. Tr7 and Tr12 clones possess type I IGF receptors, known to mediate the mitogenic effect of IGF-II, with affinity similar to those present on the membrane of the parental cells but with reduced capacity. Finally, media conditioned by Tr7 and Tr12 increase basal thymidine incorporation in quiescent FRTL5 cells and amplify that induced by TSH. Endogenous IGFs may play an important role in the regulation of thyroid cell proliferation by modulating the mitogenic effect of TSH and by supporting TSH-independent growth.

Endogenous insulin-like growth factors regulate the proliferation of TSH-independent mutants derived from FRTL5 cells.

TSH-independent mutant clones (M cells) derived from FRTL5 cells, proliferate vigorously in the absence of TSH. The growth of M cells is stimulated by IGF-I in a dose-dependent fashion, but it is not influenced by TSH. Sm1.2, an antibody against IGF-I cross-reacting with IGF-II, significantly decreases basal DNA synthesis in the M cells. Binding of 125I-IGF-I to M cells is significantly lower than that to FRTL5 cells. M cells produce in their culture medium IGF-like peptides which appear to influence their basal DNA synthesis and the availability of type I receptors to bind exogenous IGF-I.

In the thyroid cells proliferation, differentiated and metabolic functions are under the control of different steps of the cyclic AMP cascade.

In the course of studies to elucidate the complex network of interactions controlling FRTL5 cell proliferation, thyroid stimulating hormone (TSH)-independent mutants (M cells), have been obtained from FRTL5 cells by chemical mutagenesis. In the present studies, the role of TSH on the proliferation and on differentiated and metabolic functions in these mutant cells have been investigated and compared to their response to insulin-like growth factor I (IGF-I). The addition of IGF-I to M cells leads to normal stimulation of DNA synthesis. However, inspite of the fact that mutant cells display normal TSH receptors, TSH is unable to stimulate the proliferation of the M cells. Nevertheless, TSH is able to increase intracellular levels of cAMP leading to regulation of TSH function in the M cells. On the other hand, TSH does not influence iodide transport and actin filaments depolimerization in these cells. However, aminoacid transport, stimulated in wild-type FRTL5 cells by both TSH and IGFs, is under the control of IGFs but not of TSH in the mutant cells. Neither TSH or IGF-I modified the expression of c-fos proto-oncogene in the M cells, probably because of high constitutive expression. These data suggest that a crucial signalling step(s) required for TSH induced mitogenesis is impaired in the M cells, and that this signalling step is not required for IGF-I induced mitogenesis.

Abnormalities of Thyroid Function in Sjogren’s Syndrome

Siogren’s syndrome is a chronic inflammatory disease, characterized by diminished lacrimal and salivary gland secretion, the “sicca complex”, resulting in keratoconjunctivitis and xerostomia. The spectrum of the disease includes a primary form and a secondary form accompanying rheumatoid arthritis or occasionally other diseases of the connective tissue. Recent observations suggest that the incidence of both primary and secondary forms of Siogren’s syndrome is higher than previously reported (1). In addition, Sjogren’s syndrome is a disorder in which a benign autoimmune disease can terminate in a malignant lymphoid disorder. Thus, it is a “crossroad” disease that offers potential insight into the mechanism by which B-lymphocytes may become malignant. The glandular insufficiency in Sjogren’s syndrome is secondary to lymphocytic and plasmacell infiltrations. Strand and Talal (2) have recently introduced the term “autoimmune exocrinopathy” for Sjogren’s syndrome. Although the involvement of exocrine glands is the hallmark of Sjogren’s, abnormalities of thyroid function have been described among these patients (3). The aim of this study was to estimate the incidence of thyroid function abnormalities in patients with Sjogren’s syndrome. Furthermore, in preliminary experiments we examined the ability of sera from these patients to stimulate DNA synthesis in FRTL5 cells.