How to pass variables between preprocess functions
Hm...

First of all you should control order of preprocess functions execution.

preprocess_block executes earlier than preprocess_region, preprocess_region earlier than preprocess_node, and so on...

In first preprocess, you should declare static variable, like here.

$var = &amp;drupal_static('variable_name_that_will_be_placed_in_static_stack');
if (!isset($var)) {
  $var = $value_to_store;
}


So, you can access this var from later executed functions.

$var = &amp;drupal_static('variable_name_that_will_be_placed_in_static_stack');


As for your problem, it's more easy to get node from menu_router:

theme_preprocess_region(&amp;$vars)
  $node = menu_get_object();
  if ($node) {
    // get required value
  }
}