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Insulin-like growth factor-binding proteins (IGFBPs) play an integral role in modifying insulin-like growth factor actions in a wide variety of cell types. Recent evidence suggests that IGFBP-3 and IGFBP-5 also have effects on cell growth that are insulin-like growth factor-independent. In investigating possible mechanisms for this effect, the intracellular trafficking of IGFBP-3 and IGFBP-5, both of which contain sequences with the potential for nuclear localization, was studied in T47D cells. Nuclear uptake of fluorescently labeled IGFBP-3 and IGFBP-5 was observed in a proportion of T47D cells that appeared to be rapidly dividing. IGFBP-1 and IGF-BP-2, which do not possess the putative domain for nuclear translocation, were not transported to the nuclei of T47D cells. When T47D cells were preincubated with excess unlabeled IGFBP-3, nuclear localization of labeled IGFBP-3 or IGFBP-5 was not detected, indicating that their nuclear translocation involves a common pathway. Inhibition of receptor-mediated endocytosis did not affect nuclear uptake of IGFBP-3, suggesting that it uses an alternative non-classical import pathway for transport across the plasma membrane. In addition, a variant form of IGFBP-3 with a mutation in the putative nuclear localization sequence was unable to translocate to the nuclei of T47D cells, suggesting that nuclear translocation of IGFBP-3 was dependent on these carboxyl-terminal basic residues.The insulin-like growth factors (IGF-I and IGF-II) 1 are potent mitogens, which stimulate proliferation in many normal and malignant cell types (1). They bind to specific receptors, designated the type I and II IGF receptors (2), although the mitogenic effects of the IGFs are mediated through the type I IGF receptor. The IGFs also have high affinity for a family of six structurally related IGF-binding proteins, IGFBP-1 to IGF-BP-6, which are responsible for regulating the bioavailability of the IGFs in the circulation (3). The IGFBPs also modulate the activity of IGFs at the cellular level, either inhibiting or enhancing IGF action (4), and in this context are believed to be important in regulating IGF-dependent proliferation of many cancers (5).Several reports have described the growth inhibition of breast cancer cells (6) and other cell types (7) by IGFBP-3, which appears independent of activation of the type I IGF receptor. More recently, overexpression of IGFBP-3 in fibroblasts with a targeted disruption of the IGF-I receptor gene was shown to have an inhibitory effect on cell growth (8). Transforming growth factor ␤ (TGF␤) and retinoic acid, which are known to inhibit cell growth and induce apoptosis in a variety of normal and malignant cell types, also induce the expression and secretion of IGFBP-3 (5, 9). Several reports have now shown that the growth inhibitory effects of TGF␤ and retinoic acid (10, 11) and the TGF␤ induction of apoptosis (12) are mediated, at least in part, by IGFBP-3. There are fewer reports on IGF-independent action of IGFBP-5. These include the stimulation of bone ce...

To isolate a human glandular kallikrein gene, a human genomic library was screened with a probe made from a mouse kallikrein cDNA (pMK-1). Overlapping clones were obtained and nucleotide sequence determination showed that they together contained a human glandular preprokallikrein gene, hGK-1, of 5.2 kb. The gene encoded a unique preproprotein of 261 amino acids. The sequence of the mature 237-amino-acid protein had 66% homology with the sequence predicted for human kallikrein synthesized in the pancreas, kidney, and salivary gland. Moreover, it had even stronger homology (78%) with human prostate-specific antigen. The latter lacks an aspartic acid residue essential for kallikrein-specific cleavage, whereas the sequence of this new protein had all of the attributes needed to confer kallikrein-like specificity. Southern blotting indicated that the number of glandular kallikrein genes in man could be limited to three, a situation very different from mouse and rat, which each have a large multigene family. Furthermore, unlike kallikrein genes in the mouse, hGK-1 was not closely linked to other human kallikrein genes. In other respects the structure of the human kallikrein gene resembled that in mouse: coding sequences in the five exons were organized similarly, homology was higher with other members of the kallikrein gene family in the same species, and the three key amino acid residues required by serine proteases for their catalytic activity, together with the residue that confers kallikrein-specific cleavage, were conserved and located on different exons. Thus, if hGK-1 is expressed, its product represents a new, and possibly the only other enzyme with true kallikrein-like specificity in man.