Activation of the somatostatin receptor sst2 inhibits cell proliferation by a mechanism involving the stimulation of the protein-tyrosine phosphatase SHP-1. The cell cycle regulatory events leading to sst2-mediated growth arrest are not known. Here, we report that treatment of Chinese hamster ovary cells expressing sst2 with the somatostatin analogue, RC-160, led to G 1 cell cycle arrest and inhibition of insulin-induced S-phase entry through induction of the cyclin-dependent kinase inhibitor p27Kip1 . Consequently, a decrease of p27 Kip1 -cdk2 association, an inhibition of insulin-induced cyclin E-cdk2 kinase activity, and an accumulation of hypophosphorylated retinoblastoma gene product (Rb) were observed. However, RC-160 had no effect on the p21 Waf1/Cip1 . When sst2 was coexpressed with a catalytically inactive mutant SHP-1 in Chinese hamster ovary cells, mutant SHP-1 induced entry into cell cycle and down-regulation of p27Kip1 and prevented modulation by insulin and RC-160 of p27Kip1 expression, p27 Kip1 -cdk2 association, cyclin E-cdk2 kinase activity, and the phosphorylation state of Rb. In mouse pancreatic acini, RC-160 reverted down-regulation of p27Kip1 induced by a mitogen, and this effect did not occur in acini from viable motheaten (me v /me v ) mice expressing a mutant SHP-1 with markedly deficient enzymes. These findings provide the first evidence that sst2 induces cell cycle arrest through the up-regulation of p27Kip1 and demonstrate that SHP-1 is required for maintaining high inhibitory levels of p27Kip1 and is a critical target of the insulin, and somatostatin signaling cascade, leading to the modulation of p27Kip1 .

Minimal residual disease (MRD) quantification is widely used for therapeutic stratification in pediatric acute lymphoblastic leukemia (ALL). A robust, reproducible, sensitivity of at least 0.01% has been achieved for IG/TCR clonal rearrangements using allele-specific quantitative PCR (IG/TCR-QPCR) within the EuroMRD consortium. Whether multiparameter flow cytometry (MFC) can reach such inter-center performance in ALL MRD monitoring remains unclear. In a multicenter study, MRD was measured prospectively on 598 follow-up bone marrow samples from 102 high-risk children and 136 adult ALL patients, using IG/TCR-QPCR and 4/5 color MFC. At diagnosis, all 238 patients (100%) had at least one suitable MRD marker with 0.01% sensitivity, including 205/238 samples (86%) by using IG/TCR-QPCR and 223/238 samples (94%) by using MFC. QPCR and MFC were evaluable in 495/598 (83%) samples. Qualitative results (<0.01% or ≥0.01%) concurred in 96% of samples and overall positivity (including <0.01% and nonquantifiable positivity) was concurrent in 84%. MRD values ≥0.01% correlated highly (r(2)=0.87) and 69% clustered within half-a-log(10). QPCR and MFC can therefore be comparable if properly standardized, and are highly complementary. MFC strategies will benefit from a concerted approach, as does molecular MRD monitoring, and will contribute significantly to the achievement of 100% MRD informativity in adult and pediatric ALL.

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