In pituitary GH3B6 cells, signaling involving the protein kinase C (PKC) multigene family can self-organize into a spatiotemporally coordinated cascade of isoform activation. Indeed, thyrotropin-releasing hormone (TRH) receptor activation sequentially activated green fluorescent protein (GFP)-tagged or endogenous PKC1, PKC␣, PKC, and PKC␦, resulting in their accumulation at the entire plasma membrane (PKC and -␦) or selectively at the cell-cell contacts (PKC␣ and -). The duration of activation ranged from 20 s for PKC␣ to 20 min for PKC. PKC␣ and -selective localization was lost in the presence of Gö6976, suggesting that accumulation at cell-cell contacts is dependent on the activity of a conventional PKC. Constitutively active, dominant-negative PKCs and small interfering RNAs showed that PKC␣ localization is controlled by PKC1 activity and is calcium independent, while PKC localization is dependent on PKC␣ activity. PKC␦ was independent of the cascade linking PKC1, -␣, and -. Furthermore, PKC␣, but not PKC, is involved in the TRH-induced -catenin relocation at cell-cell contacts, suggesting that PKC is not the unique functional effector of the cascade. Thus, TRH receptor activation results in PKC1 activation, which in turn initiates a calcium-independent but PKC1 activity-dependent sequential translocation of PKC␣ and -. These results challenge the current understanding of PKC signaling and raise the question of a functional dependence between isoforms.Space and time parameters are intimately linked to the biological function of proteins and are pivotal in the organization and functioning of living matter. Particularly important in the case of intracellular signaling networks, this spatiotemporal constraint determines the modalities by which a given protein interacts with its partners in order to exchange information. Efforts are currently being made to translate the experimental evidence of this plasticity into a visualization concept of dynamic signaling networks (4,22). A degree of complexity is added when different isoforms of a protein coexist within the same cell and when they all potentially respond to the same stimulus, which is the case of the protein kinase C (PKC) family.The PKC family is composed of at least 11 isoforms. Several isoforms usually coexist within a given cell type, and each isoform is thought to mediate distinct cellular functions leading to proliferation, differentiation, apoptosis, or secretion. PKC function requires its translocation to a membrane compartment. The current understanding of PKC translocation/ activation has been largely based on the work of Oancea and Meyer (34), who presented conventional PKCs (cPKCs) and novel PKCs (nPKCs) as molecular machines responsible for decoding calcium and/or diacylglycerol (DAG)-mediated signals. Several observations suggest, however, that other, as yet unknown, parameters are involved in the temporal organization of PKC signaling. Indeed, despite similarities in sequence and cofactor regulation by DAG and Ca 2ϩ , the conventional P...