Highlights d PDAC regional heterogeneity stems from sub-tumor microenvironments (subTMEs) d SubTMEs exhibit distinct immune phenotypes and CAF differentiation states d SubTMEs execute distinct tumor-promoting and chemoprotective functions d Intratumoral subTME co-occurrence links stromal heterogeneity to patient outcome

Cancer cells bearing distinct KRAS mutations exhibit variable sensitivity to SHP2 inhibitors (SHP2i). Here we show that cells harboring KRAS Q61H are uniquely resistant to SHP2i, and investigate the underlying mechanisms using biophysics, molecular dynamics, and cell-based approaches. Q61H mutation impairs intrinsic and GAP-mediated GTP hydrolysis, and impedes activation by SOS1, but does not alter tyrosyl phosphorylation. Wild-type and Q61H-mutant KRAS are both phosphorylated by Src on Tyr32 and Tyr64 and dephosphorylated by SHP2, however, SHP2i does not reduce ERK phosphorylation in KRAS Q61H cells. Phosphorylation of wild-type and Gly12-mutant KRAS, which are associated with sensitivity to SHP2i, confers resistance to regulation by GAP and GEF activities and impairs binding to RAF, whereas the near-complete GAP/GEF-resistance of KRAS Q61H remains unaltered, and high-affinity RAF interaction is retained. SHP2 can stimulate KRAS signaling by modulating GEF/GAP activities and dephosphorylating KRAS, processes that fail to regulate signaling of the Q61H mutant.

L ipopolysaccharide (LPS) is an integral structural component of the outer membrane of Gram-negative bacteria and is important for the survival of these bacteria in the environment or in a host. In Pseudomonas aeruginosa and many other opportunistic pathogens, LPS is a major virulence factor and is composed of a lipid A membrane anchor, a core oligosaccharide linker, and a distal polysaccharide termed O antigen (O-Ag) (1). P. aeruginosa simultaneously produces two forms of O-Ag, a homopolymeric common antigen (CPA) and an immunodominant heteropolymeric O-specific antigen (OSA) composed of repeating trisaccharide units (2).In P. aeruginosa PAO1, OSA is synthesized via the Wzx/Wzydependent pathway (3), which requires the activity of several integral inner membrane (IM) proteins (4). Synthesis begins at the cytoplasmic leaflet of the IM on the lipid carrier undecaprenyl pyrophosphate (UndPP), with the formation of an OSA trisaccharide repeat constructed from newly synthesized nucleotide sugar precursors (5). The UndPP-linked OSA repeat is then transported through the cationic interior of the OSA flippase Wzx to the periplasmic leaflet of the IM (6, 7) and polymerized at the reducing terminus of the growing chain (8) by Wzy via a putative "catch-and-release" mechanism in an ␣-1-4 linkage (9, 10). The OSA chain length is regulated by the polysaccharide copolymerase (PCP) proteins Wzz 1 and Wzz 2 , which interact with the nascent polysaccharides and confer long (12 to 16 and 22 to 30 repeats) and very long (40 to 50 repeats) modal lengths, respectively (11,12). Full-length OSA is then ligated to the lipid A-core moiety by the O-Ag ligase WaaL (13,14), forming the mature LPS molecule.Variability in the OSA repeat sugar constituents, intra-and interglycosidic linkages of the OSA repeat residues, and the presence of side branch modifications are used to classify P. aeruginosa into 20 distinct serotypes according to the International Antigenic Typing Scheme (1). Similar OSA backbone sugar structures result in certain individual serotypes, for example, O2, O5, O16, O18, and O20, being classified into a single serogroup (serogroup O2). Immunochemical cross-reactivity of LPS of these serotypes with specific typing antisera or monoclonal antibodies (MAbs) substantiates their relatedness. In particular, the only difference between the OSA chemical structures of serotypes O5 and O16 is the ␣ or ␤ configuration of the interglycosidic bond at the reducing end, respectively (15,16). Interestingly, the OSA biosynthesis cluster spanning the pa3160 to pa3145 (wzz 1 to wbpL) genes of O5 is identical to that in serogroup O2. This suggests that genes located outside the wbp cluster are responsible for the chemical differences in the OSA structures. Therefore, genes responsible for the chemical differences in OSA structures were likely to have come from external sources such as lysogenic bacteriophage (17) or other ancestral microbial species.Serotype conversion following bacteriophage infection has long been observed in diverse . Upon i...