Giuseppina Bonizzi

The Tumor Suppressor p53 Regulates Polarity of Self-Renewing Divisions in Mammary Stem Cells

Stem-like cells may be integral to the development and maintenance of human cancers. Direct proof is still lacking, mainly because of our poor understanding of the biological differences between normal and cancer stem cells (SCs). Using the ErbB2 transgenic model of breast cancer, we found that self-renewing divisions of cancer SCs are more frequent than their normal counterparts, unlimited and symmetric, thus contributing to increasing numbers of SCs in tumoral tissues. SCs with targeted mutation of the tumor suppressor p53 possess the same self-renewal properties as cancer SCs, and their number increases progressively in the p53 null premalignant mammary gland. Pharmacological reactivation of p53 correlates with restoration of asymmetric divisions in cancer SCs and tumor growth reduction, without significant effects on additional cancer cells. These data demonstrate that p53 regulates polarity of cell division in mammary SCs and suggest that loss of p53 favors symmetric divisions of cancer SCs, contributing to tumor growth.

IKKα Provides an Essential Link between RANK Signaling and Cyclin D1 Expression during Mammary Gland Development

Abstract To identify functions of the IKKα subunit of IκB kinase that require catalytic activity, we generated an Ikkα AA knockin allele containing alanines instead of serines in the activation loop. Ikkα AA/AA mice are healthy and fertile, but females display a severe lactation defect due to impaired proliferation of mammary epithelial cells. IKKα activity is required for NF-κB activation in mammary epithelial cells during pregnancy and in response to RANK ligand but not TNFα. IKKα and NF-κB activation are also required for optimal cyclin D1 induction. Defective RANK signaling or cyclin D1 expression results in the same phenotypic effect as the Ikkα AA mutation, which is completely suppressed by a mammary specific cyclin D1 transgene. Thus, IKKα is a critical intermediate in a pathway that controls mammary epithelial proliferation in response to RANK signaling via cyclin D1 .

IκB Kinase Complex α Kinase Activity Controls Chemokine and High Endothelial Venule Gene Expression in Lymph Nodes and Nasal-Associated Lymphoid Tissue

The lymphotoxin (LT) β receptor plays a critical role in secondary lymphoid organogenesis and the classical and alternative NF-κB pathways have been implicated in this process. IKKα is a key molecule for the activation of the alternative NF-κB pathway. However, its precise role and target genes in secondary lymphoid organogenesis remain unknown, particularly with regard to high endothelial venules (HEV). In this study, we show that IKKαAA mutant mice, who lack inducible kinase activity, have hypocellular lymph nodes (LN) and nasal-associated lymphoid (NALT) tissue characterized by marked defects in microarchitecture and HEV. In addition, IKKαAA LNs showed reduced lymphoid chemokine CCL19, CCL21, and CXCL13 expression. IKKαAA LN- and NALT-HEV were abnormal in appearance with reduced expression of peripheral node addressin (PNAd) explained by a severe reduction in the HEV-associated proteins, glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1), and high endothelial cell sulfotransferase, a PNAd-generating enzyme that is a target of LTαβ. In this study, analysis of LTβ−/− mice identifies GlyCAM-1 as another LTβ-dependent gene. In contrast, TNFRI−/− mice, which lose classical NF-κB pathway activity but retain alternative NF-κB pathway activity, showed relatively normal GlyCAM-1 and HEC-6ST expression in LN-HEV. In addition, in this communication, it is demonstrated that LTβR is prominently expressed on LN- and NALT-HEV. Thus, these data reveal a critical role for IKKα in LN and NALT development, identify GlyCAM-1 and high endothelial cell sulfotransferase as new IKKα-dependent target genes, and suggest that LTβR signaling on HEV can regulate HEV-specific gene expression.

The emerging role of p53 in stem cells.

Among the hundreds of oncogenes and tumor suppressors that have been identified in the past 50 years, p53 is probably the best characterized; nevertheless, new functions are constantly being discovered. As a tumor suppressor, p53 regulates cellular responses to different stress stimuli by inducing reversible cell cycle arrest and DNA repair, or triggering senescence or apoptosis. Recent findings on the regulation of stem cell (SC) division and reprogramming suggest the intriguing possibility that p53 also carries out its tumor suppression function by regulating SC homeostasis. Specifically, p53 activation may counteract SC expansion by several emerging mechanisms including restriction of self-renewing divisions, inhibition of symmetric division and block of reprogramming of somatic/progenitor cells into SCs.

Regulation of late B cell differentiation by intrinsic IKKα-dependent signals

NF-κB-inducing kinase (NIK)-mediated IKKα phosphorylation activates the alternative NF-κB pathway, which is characterized by nuclear translocation of p52:RelB heterodimers. This alternative pathway is initiated by a select few receptors, including LT-βR, BAFF-R, and CD40. Although NIK, IKKα, and p52 are all critical regulators of LT-βR signaling in stromal cells during humoral immune responses, lymphocytes require NIK, but not p52, for optimal Ig production. This disparity suggests that NIK possesses critical cell-type-specific functions that do not depend on NF-κB. Here we use mice bearing targeted mutations of the IKKα activation loop Ser176/180 (IKKαAA) to address the B cell-intrinsic functions of NIK–IKKα signaling in vivo. We find that IKKαAA B cells mount normal primary antibody responses but do not enter germinal centers. This defect likely derives from ineffective early T–B cell collaboration and leads to impaired generation of humoral memory and relatively short-lived, low-affinity antibody production. Our findings contrast with those obtained by using p52−/− B cells, which mount normal Ig responses, and alymphoplasia (NIK mutant) B cells, which produce very little primary Ig. Thus, the NIK–IKKα–p52 axis is not as linear and exclusive as previous studies suggest, and IKKα possesses critical NF-κB-independent functions in B cells.

A Trust‐Based Pact in Research Biobanks. From Theory to Practice

Traditional Informed Consent is becoming increasingly inadequate, especially in the context of research biobanks. How much information is needed by patients for their consent to be truly informed? How does the quality of the information they receive match up to the quality of the information they ought to receive? How can information be conveyed fairly about future, non-predictable lines of research? To circumvent these difficulties, some scholars have proposed that current consent guidelines should be reassessed, with trust being used as a guiding principle instead of information. Here, we analyse one of these proposals, based on a Participation Pact, which is already being offered to patients at the Istituto Europeo di Oncologia, a comprehensive cancer hospital in Milan, Italy.

Setting sights on the right target: p53 and stem cell division

Abstract not yet available.