Asymmetric divisions are crucial for generating cell diversity; they rely on coupling between polarity cues and spindle positioning, but how this coupling is achieved is poorly understood. In one-cell stage Caenorhabditis elegans embryos, polarity cues set by the PAR proteins mediate asymmetric spindle positioning by governing an imbalance of net pulling forces acting on spindle poles. We found that the GoLoco-containing proteins GPR-1 and GPR-2, as well as the Galpha subunits GOA-1 and GPA-16, were essential for generation of proper pulling forces. GPR-1/2 interacted with guanosine diphosphate-bound GOA-1 and were enriched on the posterior cortex in a par-3- and par-2-dependent manner. Thus, the extent of net pulling forces may depend on cortical Galpha activity, which is regulated by anterior-posterior polarity cues through GPR-1/2.

Patients with human papillomavirus associated (HPV+) head and neck cancer (HNC) demonstrate significantly improved survival outcome compared to those with HPV− negative (HPV−) tumors. Published data examining this difference offers conflicting results to date. We systematically investigated the radiation sensitivity of all available validated HPV+ HNC cell lines and a series of HPV− HNC cell lines using in vitro and in vivo techniques. HPV+ HNCs exhibited greater intrinsic radiation sensitivity (average SF2 HPV− 0.59 vs. HPV+ 0.22, p<0.0001), corresponding with a prolonged G2/M cell cycle arrest and increased apoptosis following radiation exposure (percent change 0% vs. 85%, p=0.002). A genome-wide microarray was used to compare gene-expression 24 hours following radiation between HPV+ and HPV− cell lines. Multiple genes in TP53 pathway were upregulated in HPV+ cells (Z score 4.90), including a 4.6 fold increase in TP53 (p<0.0001). Using immortalized human tonsillar epithelial cells, increased radiation sensitivity was seen in cell expressing HPV-16 E6 despite the effect of E6 to degrade p53. This suggested that low levels of normally functioning p53 in HPV+ HNC cells could be activated by radiation, leading to cell death. Consistent with this, more complete knockdown of TP53 by siRNA resulted in radiation resistance. These results provide clear evidence, and a supporting mechanism, for increased radiation sensitivity in HPV+ HNC relative to HPV− HNC. This issue is under active investigation in a series of clinical trials attempting to de-escalate radiation (and chemotherapy) in selected patients with HPV+ HNC in light of their favorable overall survival outcome.

Abstract. Heterotrimeric G-proteins are intracellular partners of G-protein-coupled receptors (GPCRs). GPCRs act on inactive Ga·GDP/Gbg heterotrimers to promote GDP release and GTP binding, resulting in liberation of Ga from Gbg. Ga·GTP and Gbg target effectors including adenylyl cyclases, phospholipases and ion channels. Signaling is terminated by intrinsic GTPase activity of Ga and heterotrimer reformation -a cycle accelerated by 'regulators of G-protein signaling' (RGS proteins). Recent studies have identified several unconventional G-protein signaling pathways that diverge from this CMLS, Cell. Mol. Life Sci. 62 (2005) 551-577 1420-682X/05/050551-27 DOI 10.1007/s00018-004-4462-3 © Birkhäuser Verlag, Basel, 2005 CMLS Cellular and Molecular Life Sciencesstandard model. Whereas phospholipase C (PLC) b is activated by Ga q and Gbg, novel PLC isoforms are regulated by both heterotrimeric and Ras-superfamily G-proteins. An Arabidopsis protein has been discovered containing both GPCR and RGS domains within the same protein. Most surprisingly, a receptor-independent Ga nucleotide cycle that regulates cell division has been delineated in both Caenorhabditis elegans and Drosophila melanogaster. Here, we revisit classical heterotrimeric G-protein signaling and explore these new, non-canonical G-protein signaling pathways.