Hyperinsulinemia is a probable trigger for weight gain and hyperphagia in individuals with Prader-Willi syndrome.

Objective: Prader-Willi syndrome (PWS) is the most frequently diagnosed genetic cause of early childhood obesity. Individuals with PWS typically progress through 7 different nutritional phases during their lifetime. The main objective of this study was to assess potential factors, particularly insulin, that may be responsible for the weight gains in sub-phase 2a and their role in the subsequent increase in fat mass and obesity in sub-phase 2b and insatiable appetite in phase 3. Methods: Fasting plasma insulin levels were measured in children with PWS between the ages of 0-12 years and in age-matched non-PWS participants with early-onset major (clinically severe) obesity (EMO) and in healthy-weight sibling controls (SC). Results: Participants with PWS in nutritional phases 1a and 1b had plasma insulin levels comparable to SC. However, the transition from phase 1b up to phase 3 in the PWS group was accompanied by significant increases in insulin, coinciding in weight gains, obesity, and hyperphagia. Only individuals with PWS in phase 3 had comparable insulin levels to the EMO group who were higher than the SC group at any age. Conclusions: Elevated insulin signaling is a probable trigger for weight gain and onset of hyperphagia in children with Prader-Willi syndrome. Regulating insulin levels early in childhood before the onset of the early weight gain may be key in modulating the onset and severity of obesity and hyperphagia in individuals with PWS, as well as in other young children with non-PWS early-onset obesity. Preventing or reversing elevated insulin levels in PWS with pharmacological agents and/or through diet restrictions such as a combined low carbohydrate, low glycemic-load diet may be a viable therapeutic strategy in combating obesity in children with PWS and others with early childhood obesity.

Hyperghrelinemia in Prader-Willi syndrome begins in early infancy long before the onset of hyperphagia.

Circulating total ghrelin levels are elevated in older children and adults with Prader-Willi syndrome (PWS). However, the presence or absence of hyperghrelinemia in young children with PWS remains controversial. We hypothesized that a more robust way to analyze appetite-regulating hormones in PWS would be by nutritional phases rather than age alone. Our objectives were to compare total serum ghrelin levels in children with PWS by nutritional phase as well as to compare total ghrelin levels in PWS (5 weeks to 21 years of age) to normal weight controls and individuals with early-onset morbid obesity (EMO) without PWS. Fasting serum total ghrelin levels were measured in 60 subjects with PWS, 39 subjects with EMO of unknown etiology, and in 95 normal non-obese sibling controls of PWS or EMO subjects (SibC) in this 12 year longitudinal study. Within PWS, total ghrelin levels were significantly (P < 0.001) higher in earlier nutritional phases: phase 1a (7,906 ± 5,887); 1b (5,057 ± 2,624); 2a (2,905 ± 1,521); 2b (2,615 ± 1,370) and 3 (2,423 ± 1,350). Young infants with PWS also had significantly (P = 0.009) higher total ghrelin levels than did the sibling controls. Nutritional phase is an important independent prognostic factor of total ghrelin levels in individuals with PWS. Circulating ghrelin levels are elevated in young children with PWS long before the onset of hyperphagia, especially during the early phase of poor appetite and feeding. Therefore, it seems unlikely that high ghrelin levels are directly responsible for the switch to the hyperphagic nutritional phases in PWS.

Analysis of steroid hormone effects on xenografted human NF1 tumor schwann cells.

The neurofibroma, a common feature of neurofibromatosis type 1 (NF1), is a benign peripheral nerve sheath tumor that contains predominantly Schwann cells (SC). There are reports that neurofibroma growth may be affected by hormonal changes, particularly in puberty and pregnancy, suggesting an influence by steroid hormones. This study examined the effects of estrogen and progesterone on proliferation and apoptosis in a panel of NF1 tumor xenografts. SC-enriched cultures derived from three human NF1 tumor types (dermal neurofibroma, plexiform neurofibroma, and malignant peripheral nerve sheath tumor (MPNST)) were xenografted in sciatic nerves of ovariectomized scid /Nf1-/+ mice. At the same time, mice were implanted with time-release pellets for systemic delivery of progesterone, estrogen or placebo. Proliferation and apoptosis by the xenografted SC were examined two months after implantation, by Ki67 immunolabeling and TUNEL. Estrogen was found to increase the growth of all three MPNST xenografts. Progesterone was associated with increased growth in two of the three MPNSTs, yet decreased growth of the other. Of the four dermal neurofibroma xenografts tested, estrogen caused a statistically significant growth increase in one, and progesterone did in another. Of the four plexiform neurofibroma SC xenografts, estrogen and progesterone significantly decreased growth in one of the xenografts, but not the other three. No relationship of patient age or gender to steroid response was observed. These findings indicate that human NF1 Schwann cells derived from some tumors show increased proliferation or decreased apoptosis in response to particular steroid hormones in a mouse xenograft model. This suggests that anti-estrogen or anti-progesterone therapies may be worth considering for specific NF1 neurofibromas and MPNSTs.

Neurofibromin physically interacts with the N-terminal domain of focal adhesion kinase.

The NF1 gene that is altered in patients with type 1 neurofibromatosis (NF1) encodes a neurofibromin protein that functions as a tumor suppressor. In this report, we show for the first time physical interaction between neurofibromin and focal adhesion kinase (FAK), the protein that localizes at focal adhesions. We show that neurofibromin associates with the N-terminal domain of FAK, and that the C-terminal domain of neurofibromin directly interacts with FAK. Confocal microscopy demonstrates colocalization of NF1 and FAK in the cytoplasm, perinuclear and nuclear regions inside the cells. Nf1+/+ MEF cells expressed less cell growth during serum deprivation conditions, and adhered less on collagen and fibronectin-treated plates than Nf1(-/-) MEF cells, associated with changes in actin and FAK staining. In addition, Nf1+/+ MEF cells detached more significantly than Nf1(-/-) MEF cells by disruption of FAK signaling with the dominant-negative inhibitor of FAK, C-terminal domain of FAK (FAK-CD). Thus, the results demonstrate the novel interaction of neurofibromin and FAK and suggest their involvement in cell adhesion, cell growth, and other cellular events and pathways.

Focal adhesion kinase and cancer.

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that resides at the sites of integrin clustering, known as focal adhesions. The FAK protein has a molecular mass of 125kDa and is encoded by the FAK gene located on human chromosome 8q24. Structurally, FAK consists of an amino-terminal regulatory FERM domain, a central catalytic kinase domain, two proline-rich motifs, and a carboxy-terminal focal adhesion targeting domain. FAK has been shown to be an important mediator of cell growth, cell proliferation, cell survival and cell migration, all of which are often dysfunctional in cancer cells. Our lab was the first to isolate FAK from primary human tissue and link it to the process of tumorigenesis. We analyzed FAK mRNA expression in normal, invasive and metastatic human tissues and demonstrated through Northern blot analysis that normal tissues had very low levels of FAK mRNA while primary and metastatic tumors significantly overexpressed FAK. We also demonstrated and confirmed FAK overexpression in colorectal carcinoma and liver metastases with real-time PCR. In this review we summarized immunohistochemical data of FAK expression and role in different cancer types tumors and discussed FAK inhibition therapy approaches.

A small molecule inhibitor, 1,2,4,5-benzenetetraamine tetrahydrochloride, targeting the y397 site of focal adhesion kinase decreases tumor growth.

Focal adhesion kinase (FAK) is a nonreceptor kinase that is overexpressed in many types of tumors. We developed a novel cancer-therapy approach, targeting the main autophosphorylation site of FAK, Y397, by computer modeling and screening of the National Cancer Institute (NCI) small molecule compounds database. More than 140,000 small molecule compounds were docked into the N-terminal domain of the FAK crystal structure in 100 different orientations that identified 35 compounds. One compound, 14 (1,2,4,5-benzenetetraamine tetrahydrochloride), significantly decreased viability in most of the cells to the levels equal to or higher than control FAK inhibitor 1a (2-[5-chloro-2-[2-methoxy-4-(4-morpholinyl)phenylamino]pyrimidin-4-ylamino]-N-methylbenzamide, TAE226) from Novartis, Inc. Compound 14 specifically and directly blocked phosphorylation of Y397-FAK in a dose- and time-dependent manner. It increased cell detachment and inhibited cell adhesion in a dose-dependent manner. Furthermore, 14 effectively caused breast tumor regression in vivo. Thus, targeting the Y397 site of FAK with 14 inhibitor can be effectively used in cancer therapy.

p53 regulates FAK expression in human tumor cells.

Attenuation of the p53 protein is one of the most common abnormalities in human tumors. Another important marker of tumorigenesis is focal adhesion kinase (FAK), a 125-kDa tyrosine kinase that is overexpressed at the mRNA and protein levels in a variety of human tumors. FAK is a critical regulator of adhesion, motility, metastasis, and survival signaling. We have characterized the FAK promoter and demonstrated that p53 can inhibit the FAK promoter activity in vitro. In the present study, we showed that p53 can bind the FAK promoter-chromatin region in vivo by chromatin immunoprecipitation (ChIP) assay. Furthermore, we demonstrated down-regulation of FAK mRNA and protein levels by adenoviral overexpression of p53. We introduced plasmids with different mutations in the DNA-binding domain of p53 (R175H, p53 R248W and R273H) into HCTp53(-/-) cells and showed that these mutations of p53 did not bind FAK promoter and did not inhibit FAK promoter activity, unlike wild type p53. We analyzed primary breast and colon cancers for p53 mutations and FAK expression, and showed that FAK expression was increased in tumors containing mutations of p53 compared to tumors with wild type p53. In addition, tumor-derived missense mutations in the DNA-binding domain (R282, R249, and V173) also led to increased FAK promoter activity. Thus, the present data show that p53 can regulate FAK expression during tumorigenesis.